If rappers get their own thread, why not give this a try? I lack any skills in rhyming and prefer rock and blues anyways. I respect opinions so long as you don't say Lil Wayne or John Mayer.

1. Jimi Hendrix (Yes, technically he was a mess I'll admit that, but he was far ahead of his time and had huge influence over every future guitarist.)
2. Stevie Ray Vaughan (Honestly not sure if he's better then others like Duane Allman, but he had some incredible skill and was practically Hendrix reborn even if he didn't believe so)
3. Duane Allman (everybody says this)
4. Eric Clapton (Also everybody says this)
5. B.B. King (He's the grandfather of electric guitar. Say nothing else)

In no particular order:

Jimi Hendrix
Eric Clapton
Jimmy Page
Eddie Van Halen
Carlos Santana

Obviously there are a ton of great guitarists, but these were sort of the first 5 I thought of off the top of my head.

Eddie Van Halen... nuff said

Prince is the only one that comes to mind.

^Respectable guitarist, but I don't dig his arrogance.

Cliff Burton.
Joe Satriani
Jimmy Hendrix

Hendrix
Ry Cooder
Dave Gregory (XTC)
David Gilmour
Frank Zappa

I'm mad at myself for forgetting Zappa. Definitely one of the most innovative guitarists out there (though in that category I must add Thurston Moore and Lee Ranaldo.)

Lil Wayne is the best.

Try harder.

I'm not very good at this.

A lot of you named the more obvious ones, so I will go into the more Progressive/obscure side of things. Also, I know I exceeded 10, but there are just too many amazing guitarists not to mention.

Allan Holdsworth (Tony Williams Lifetime, Soft Machine, Jean-Luc Ponty, Gong, U.K.)
Andrew Latimer (Camel)
Steve Howe (Yes, Asia)
Robert Fripp (King Crimson)
Steve Hackett (Genesis)
Jan Akkerman (Focus)
Jeff Beck (Solo, Yardbirds, Jeff Beck Group)
John McLaughlin (Mahavishnu Orchestra)
Steve Hillage (Khan, Gong, Solo)
Todd Rundgren (Solo, Utopia, Nazz)
Adrian Belew (King Crimson, Zappa, Adrian Belew Power Trio, Solo)
Greg Lake (Emerson, Lake and Palmer, King Crimson)
Al Di Meola (Solo, Return to Forever)
Daryl Stuermer (Jean-Luc Ponty, Gino Vanelli)
John Goodsall (Brand X)
Paco de Lucia (Solo)
Tony Iommi (Black Sabbath, Heaven and Hell)
Ritchie Blackmore (Deep Purple, Rainbow)
K.K. Downing and Glenn Tipton (Judas Priest)
Dave Murray, Adrian Smith and Janick Gers (Iron Maiden)
Tosin Abasi (Animals As Leaders)

^Good job on reminding me of Jeff Beck. Damn, I keep forgetting stuff. I knew something was wrong when Beck (of Loser fame) popped into my head for this thread.

1.B.B King

2.Jimi Hendrix

3.Prince

4.Gene Simmons

Dimebag Darrel from Pantera

PANTERA - Cemetery Gates

PANTERA - Shedding Skin

PANTERA - This Love

PANTERA - 5 Minutes Alone

PANTERA - I'm Broken

PANTERA - Floods

Jason Becker
Paul Gilbert
Marty Friedman
I consider those three to be in a league of their own.

Jack White, Jimi Hendrix, Eddie Van Halen.

I'll just mention a couple which have been glossed over so far in this thread

Tommy Emmanuel (amazing fingerpicker, tends to play 2-3 guitar lines on a single six-string. Comes off as a bit showoff-y, but you'll understand his talent if you try to learn one of his songs) http://www.youtube.com/watch?v=KNuwJbgnkIE

Terry Kath (Guitarist from Chicago, who tragically died before the band really hit mainstream success with a stream of wedding-ballads. Kath played anything from blues runs to jazz comping, and was respected even by Jimi Hendrix) http://www.youtube.com/watch?v=up3eXOV3JqY

John Butler (Street guitarist from Australia, who plays an 11 string, often with slide. Weird combination, but it's really interesting to listen to.) http://www.youtube.com/watch?v=6VAkOhXIsI0

And obligatory mention to Duane Allman, Ry Cooder, Jimi Hendrix, Eric Clapton, etc there are too many great ones to name

Tom Morello from Rage Against The Machine

RATM - Bombtrack live

RATM - Killin' In The Name live

RATM - Bulls On Parade live

RATM - Take The Power Back

RATM - Know Your Enemy

from yesteryear: hendrix, clapton, g. harrison

today: morello, even better is miyavi, who is amazing.