So my school is doing a talent show-ish thing called Artasia and a friend of mine from choir wants to sing in it with some other people and she wants me to play guitar, and I agreed.

She was thinking of doing either Wonderwall or Iris. Both of which are good songs and I wouldn't mind playing them, but I was hoping for something that doesn't make me look like an idiot who can only play those songs, if you know what I mean.

So, any good suggestions for acoustic songs that would sound good with three girls singing, and have at least some mild semblance of difficulty?

I would just look through the song suggestions thread but this is kind of a more specific request.

My Guitars:
Fender Mustang.
Yamaha FG-413SL.
Maybe look into some Heart. The acoustic intro from Crazy on You is pretty wild. That or maybe do an acoustic version of a song you like that isn't normally played on acoustic.

Gotta say I can understand not wanting to be "that guy" playing Wonderwall
-Guitar Gear-
1995 American Fender Strat, EMG 85 pup
Randall RH200 Head
Marshall 1960a Cab
Woods Acoustic
-Bass Gear-
Spector Legend 4 bass
Washburn Bantam bass
Hartke HA2500
Fender Bassman 410H
Play what you love, love what you play
Tears in Heaven, and have the girls do a harmony if they're good at singing. Definitely like Garou said, Heart is another good band.
try Angie by the Stones. Its a cool little fingerpicking tune that'll probably sound good with girls singing.
try some songs by mariah carey.. those are usually in piano but put them into a guitar and add some scales and it will sound good.. try also some oldies like james taylor.. romantic and mellow songs with very good intros and chord patterns..
Doesn't have to be difficult to be good (i.e. Dylan).

I think, One- U2, would sound good with the girls.
Drive by Incubis?
Say It Ain't So by Weezer? (I always thought it sounded nice on acoustic)
My My Hey Hey by Neil Young?
Behind Blue Eyes by The Who?
Across the Universe by The Beatles?
Oh by Dave Matthews Band?
Hotel California by Eagles?
Wake Me Up When September Ends by GreenDay? (There's a space between green & day isn't there )
Heard the World by OAR?

Hope that helps
Iris and Wonderwall... are these the only songs girls know these days!?
Les Paul Black Beauty Custom 3 Pickup
Bigsby B7g vibrato
3 EMG's 85/81/85

Martin D-28