Harder Sound:

Vocals-Chris Cornell in his hayday (Badmotorfinger, Superunknown)
Lead Guitar-Jerry Cantrell (Alice in Chains)
Rhythm Guitar-Omar Rodriguez-Lopez (The Mars Volta)
Bass-John Entwistle (The Who)
Drums-Bill Ward (Black Sabbath)

Softer Sound:

Vocals-Stevie Nicks, Devendra Banhart or Sam Beam
Guitar 1-Johnny Greenwood (Radiohead)
Guitar 2-Andy Summers (The Police)
Bass-Roger Waters (Pink Floyd)
Keys-Thom Yorke (Radiohead)
Drums-Michael Giles (King Crimson)

Vocals/Lyrics - Serj Tankian/Daron Malakian
Piano/Keyboards/Composer - Matt Bellamy
Lead Guitar - A.J. Minette
Rhythm Guitar - Thomas Erak (I think he and A.J would blend into something awesome, given the fact that this would actually be a functioning band)
Bass Guitar - Arif Mirabdolbaghi
Drums - Dominic Howard

Five-Piece?
No way, I'd make a post rock band and call it Explosions In The Sky.

Thank God.

Can't remember whether or not I've done one of these before, but I've got some time to kill so...

Nick Cave - vocals
Robert Fripp - guitar
Johnny Marr - guitar
Matt Johnson - keyboards/synth, backing vocals
Bruce Thomas - bass
Jaki Liebezeit - drums/percussion

And they'd be called the Emperor's New Spandex or something like that.

Rock band:

to be honest i would just pick nirvana but that's me so i will mix it up.

Singer - Kurt Cobain
Guitar - Tom Morello
Bass - Flea
Drums - Danny Carry

Metal band:

Singer - i couldn't decide so i'm picking two and it could be a cool combination actually between them. alissa white-gluz and serj tankian
Guitar - Dimebag
Bass - Karin Axelsson
Drums - Joey Jordison

Meg White on drums

Sid Vicious on bass

Yngwie Malmsteen on guitar

DJ Lethal on turntables

and William Shatner on vox

They would be called Spunksock and they would rock the ass off the world.

William Shatner... Nice choice.

Nahhh

Derek Smalls

Only if he brings his pod.