OK. I thought it might be a fun exercise to compare notes on who and how you would line up your team for their 1st match of the season. I guarantee that there will be such variety even for the same teams. Here are a few simple Guidelines:
RULE #1 - You may ONLY pick players that are currently on your roster and are not injured (or if injured expected to be fit within the next few days). In other words, if you are a RM fan you may not include Modric, and so on....
RULE #2 - If you would choose the exact same line-up as a previous poster simply say "I agree with so and so" to avoid redundancy
SUGGESTION #1 - The team can be your ideal 1st 11 for the season or one that
it more catered to your opponent on opening match day. For example, if
you are playing against Stoke City you may want to choose a Defensive
midfielder that you wouldn't otherwise include. You get the idea

SUGGESTION #2 - If you pick a player or formation that is non-conventional it
would be best if you summarize your reason in a quick line
SUGGESTION #3 - I would like to see as much of a variety of teams as is possible so try to get involved. I would like to avoid an entire thread of only Arsenal, Manchester United & Barcelona line-ups. Lastly, if you think you have a good suggestion for a team besides the one you follow feel free to add that as well.
Let's see what you got!

    Cech
Cole-Terry-Cahill-Ivanovic
    Mata-Oscar-Lampard 
      Hazard- Torres- Marin

Subs: Turnbull
          Essien
          Mikel
          Luiz
          Malouda
          Bertrand
          Sturridge

@ChelseaRox, where is Meireles? lol..

Formation: 4-3-1-2

                          Valdes
              Alves-Pique-Puyol-Alba
                           Xavi
                Sanchez----Iniesta
                         Fabregas
                    Villa-----Messi

Substiutions:

Adriano
Afellay
Tello
Muniesa
Pinto

@Footaholic , yes i forgot then we put Samuel as a replace for him 

as you said there's a lot of suiside line-up from barça fans...

Tito Vilanova will play with 2 tipe of line-ups:

The classic one: 
                            V.Valdes
D. Alves - Pique - Puyol(Mascherano) - J. Alba (Adriano)

                 S. Busquets (Mascherano)
           Xavi (Fabregas)            A. Iniesta (Afellay, Thiago)
A.Sanchez (Pedro)                         Villa(Tello) 
                         L. Messi (Fabregas)    

The 3-4-3 one: 

                           V.Valdes
 Pique      -    Puyol(Mascherano) - J. Alba (Adriano)

                 S. Busquets (Mascherano)
D. Alves   -  Xavi (Fabregas)  -  A. Iniesta (Afellay, Thiago)
A.Sanchez (Pedro)         -                Villa(Tello) 
                         L. Messi (Fabregas)    

Wanna or not, Hate or not, but Busquests is a fundamental piece in the barça's line up. 

My Arsenal XI in the first match:

Formation: 4-2-3-1

GK: Fabianski (Why him? well i am just guessing that is the first match and is against Sunderland, plus Szczesny player against Cologne so  maybe AW would like to show Szczesny that there is still competition for the GK spot -I would do that as Arsenal manager- so hoping that Wojciech would just improve his skills for that spot.)

RB: Coquelin (As Footaholic said i preffer him in that spot, Jenkinson is a bit to weaky and Yennaris is way to young and i like Yennaris more in a Midfield position.)

CB: Mertesacker and Vermaelen (Mertesacker is getting fit so maybe he would just improve and become a good defender once he make it to stabilish in the PL way to play, and  Vermalene because he is the Verminator.)

LB: Santos (I would lke to choose Gibbs over him but Santos has that thing that probably can solve you a match, also in his adventures as a wingr maybe we could watch a more attacking Santos helping the left winger in that position.)

CDM: Song

CM: Arteta (I am sure he is going to play like a false ATM but coming from the back, i'l explain myself; h is going to recover the ball in the back of the midfield with Song helping him and then he is going to get to the top with the ATM helping him in the creation.)

ATM: Cazorla (Playing a role behind the ST and creating, having to choose not only the ST to play, but the wingers AND Arteta who i hope is going to play the way i stated before.)

LW: Podolski (In here i don't agree with you Footaholic, i really think that AW is going to play Poldi at least the first half so Sunderland and the other ones watching knows that we are not just messing around this season. But if is not then Chambo or Gervinho would play, i preffer Chambo.)

RW: Walcott

ST: Giroud (Hoping him to score his first goal of the season with us, looked well against Cologne but lacked finishing, maybe this match would be his match.

NOTE: I don't want van Persie to play but i expect him to play, how is this? well you all know Wenger he doesn't like to waste talent.

@Footaholic

I would choose Afellay over Villa because he has played a good pre-season. I think his way of playing looks more confident compared to his start at Barça. He also has got a great shot from range.

About the 3-4-3 formation, I chose this because Guardiola also did a couple of times last season. It looked very promising, and even more offensive! 

My opinion on Real's opening match against Valencia

GK: Casillas

RB: Arbeloa

CB: Ramos & Pepe (I've seen ppl put Ramos as right back but honestly, Carvalho is too old to keep marking people like Soldado and Jonas for a whole match. Plus, Ramos has proved more efficient at Cb than RB, to the point where he even became Spain's CB (although that was partially due to Puyol's absence))

LB: Marcelo/Coentrao (there is a reason why i am unsure about LB. it depends on what mourinho has planned for valencia. he usually prefers Marcelo against Valencia since he gets more offence with Marcelo but if he changes his tactics he might end up using the defensive Coentrao. Additionally, Coentrao has impressed greatly in the EURO 2012 Finals offensively and defensively, but Marcelo has better teamwork with Ronaldo who is on the same wing as him)

DM: Alonso and Khedira (no complaints there, although giving Lass and Granero more chances would be nicer)

AM: Ozil (honestly, Kaka was a fabulous player but he is inconsistent now. he will do amazing in some games and then flop down on the next. i don't think Mourinho will want to take that bet so Ozil looks like the first pick. IMO, Ozil would have been chosen anyway because he is better than Kaka atm)

LM: Ronaldo

RM: di Maria (its true that Callejon has impressed greatly in the pre season but Mourinho will have to take advantage of Alba's disappearance in the squad. Mathieu is Valencia's new first choice LB and he is much bigger and slower than Alba. di Maria's quick dribbling can be used efficiently down that wing. i expect to see Callejon later on in the game as a sub, tho)

ST: Benzema (like the others said... he's more goal hungry than Higuain)

@nico - Spot On! either of those are definitely more balanced line-ups. @thijsFCB My question wasn't regarding the formation but the fact that you left out a defensive midfielder. See nico's line-ups to understand. 3-4-3 is already an overly-attacking formation and so leaving out a proper DM (which Xavi & Fabregas are not) would be VERY dangerous. IMO you need Busquets in there.

@Golden & @Dynastian: Can I just posit that I believe Coentrao is by far, and away, a better LB than Marcelo. Marcelo is fast and may provide excellent attacking support but I don't rate him as a defender. But perhaps I'm biased because I also think he's a prick.

@GunnerGo - Few Points:
-Great idea about stoking the GK competition. Personally, I think Fabs is actually a decent GK. It is Mannone that I think isn't good enough and should probably look elsewhere as he'll get nowhere near the 1st team especially with young Martinez soon to force his way into the reckoning.
-Regarding RB, while Santos can certainly win you a game, he's just as likely (if not more so) to lose you a game.
-Your description of Arteta is that of a "box-to-box midfielder". He is certainly capable of doing this but there are others that are better at this particular job (e.g. Diaby).
-I don't know about you but I would've liked RVP to start the season because I'd rather phase Giroud in slowly. He didn't look completely sharp in the last match and hasn't had many minutes under his belt yet. I am a bit worried he'll struggle the first few matches but it looks like we won't have a choice anyway as RVP looks set to be a player of the past :(

4-2-3-1Cech
Ivanovic-Cahill-Terry-Ashley
Mikel/Essien-Lampard
Ramires-Mata-Hazard
Torres

Subs:
Sturridge
Essien
Oscar
David Luiz
Bertrand
Raul M.

@Footaholic: You know it would be dangerous to play Giroud in the first minutes now that i think it better, Giroud hasn't got real time play, so maybe we would see van Persie starting? if that's so, how you imagine he would feel when he see Vermaelen with the Captain armband? i think i got some place in my hearth for RVP at last...

@Footaholic I totally agree with this starting XI, but I think Santos will be better choice for LB than Gibbs.

4-2-3-1

                   Cech
Ivanovic - Luiz - Terry - Cole
         Ramires - Lampard
      Mata - Oscar - Hazard
                 Torres

Now that RVP came to United, I think my formation doesn't work. :P

4-2-3-1

GK : Szczesny, simply because he is better than fabiansky.

RB : I agree with footaholic on Coquelin. Best choice for RB while we wait for Sagna

CB : Mertesacker + Verm. Kosc was touched during the game against cologne, should be back for our next game.

LB : Gibbs, more defensive than santos, it's the start of the season, sometimes people are clunky and things go wrong, especially with santos.

CDM : Song, no real discussion here.

CM : Arteta. He was our best midfielder last year, I liked him even more than song. Diaby would also be a good choice to have a more physical midfield but we haven't seen him play this year yet (apart from friendlies).

ATM : Cazorla. Rosicky is still injured (if i'm correct), we have ramsey, but we spent 17m on Cazorla so why not make him play and see what he is really worth.

LW : Podolski. Great game against cologne, great signing.

RW : Walcott. I still like him more than the Ox. Scored many important goals last season like against Chelsea or Spurs.

ST : Giroud. No more RVP. Giroud was one of my favourite Ligue 1 players last year. So I want him to play great and score on his EPL debut.

@chelsearox Where is ramirez ? and Meireles ? I had to read your post 3 times to make sure i had read correctly. Ramirez was amazing last season, and meireles one of my favorite players during the euro.

I've really enjoyed reading your posts and it's turning into one of the best threads I've read. Some interesting formations that I would have never thought of! Plus, as you can see almost everyone has a different lineup for their teams (even if by 1 player).  So far we've seen United, Barca, RM, Spurs, Arsenal, Chelsea, Valencia, Inter, & Liverpool. That a good collection but I'd really like to see MORE VARIETY. Where's my AC Milan, Juve, Bayern, Dortmund, Shalke, Porto, Sporting, PSG, Lyon supporters? C'mon guys lets KEEP THIS GOING!

so, this for you Footaholic

Bayern Munich

                       Neuer
Lahm - Boateng - Badstuber - Alaba
                 Schweinsteiger
   Robben - Shaqiri - Kroos - Ribery
                        Gomez

AC Milan

                   Abbiati
Abate - Zapata - Mexes - Vila
      Montolivo - Nocerino
                 Boateng
Cassano                  Emanuelson 
                    Pato

as i dun like that khedira :S

my formation will be 4-1-3-2

                            Casillas

Arbeloa          Pepe           Ramos        Marcelo

                             Alonso

Di Maria               Ozil /Kaka                 Ronaldo

                 Higuain             Benzema

@JuanMata:
Thank you. Looks Milan looks about right (I think they might be a bit easier to predict these days). As for bayern, I think your line-up would work well against the Fruth (their first match). Just for my own curiosity how would you line them up against a more talented side (say a good CL side)? Would your play Muller instead of Shakiri in that formation? For me, I'd put Gustavo (who I highly rate) or Kroos as a DM next to Shweini in a 4-2-3-1. I think 4-1-4-1 might be a bit too gung-ho.

@ironfist: I quite like that formation against less dangerous sides. I wonder does Mourinho ever employ it (b/c I can't seem to remember him doing that off the top of my head)?