Since we are stating opinions, I thought I would add my own.
Alex Skolnick- Put down allot of great guitar work with Testament and a great stand in with Savatage.
Mike Romeo- I am sure I missed his mention being on this forum. If not shame on you.
Steve Stevens- I got a chance to catch him with Vince Neil and Billy Idol back in the day. An unbelieveable player to say the least.
Nuno Bettencord- Prob the most underrated player, along with Chris Oliva, to ever play guitar.
Olaf Lenk- At Vance is one of those bands I really used to like. However, his guitar work is worth buying the disc for.
Thomas Youngblood- I didn't realize how good he is till I saw them live, Shredder!!
Jeff Loomis- I just thought he needed mentioning again.
Reb Beach- The guy is awesome.
Adrian Vandenberg- Not a great player, but very solid. I add him to the list for simply being the definition of metal. Check out some Whitesnake videos, this guy is Metal!
This list could go on and on, very cool thread though!