Good call Ken. I have some old video footage of Marillion playing Forgotten Sons live and Rothery sounds incredible; he's using a Yamaha SG with what look like DiMarzios in it. As for the other 2, Yes and Genesis from ATTWT backwards are 2 of my absolute favourite bands of all time...in fact Yes are arguably my favourite, although Seconds Out is probably my most played album. Regarding my earlier mention of Andy Latimer and Dave Gilmour, Moonmadness is probably my favourite album of all time, with Wish You Were Here there or thereabouts.

Don't think I'm adding much new but I saw Brian May's name up there an have to agree.  Also, Mark Knopfler on Sultans of Swing is one of my favorites for tone quality though there are a couple points there in the solos where I wish he'd had a little more sustain.  Nuno Bettencourt on Extreme's 3rd album had incomparable tone.

I was doing a little reading on Jimi Hendrix and found it interesting that two of his favorite guitarist were, Terry Kath and Billy Gibbons.  
 
Very different styles but both very good players.
 
In fact that got me to bust out my CTA and Chicago II CD's. Some pretty incredible guitar work on both.

Well, to add someone whom I always am attracted to, Chet Atkins.  'nuff said

Chet was deffinately a great player Roger. There are a lot of overlooked players in the country scene. Roy Clark, Merle Haggard, Steve Warriner just to name a few.  
These guys don't really get rocognized as guitar players too much but I've seen them all live and was very impressed with their skills. All 3 of the above play several different instruments too.
 
Probably the fastest clean guitar I've ever heard though was PeeWee Oliver. Played a 4 string tenor guitar (mandolin was his first instrument) and walked circles around guys on a 6 string.

Well, for rock tones it has to be;
Leslie West on Mississippi Queen (studio version)
Leslie again on the live version of dream sequence---the last 2 chords of his solo part are still the most powerful I've EVER heard.
Paul Kossoff on the Free Tons of Sobs album.
SRV playing Little Wing
Roy Buchanan on Wayfaring Pilgrim.
Jeff Beck on Because we've ended as lovers
For grunge bass;
Jack Bruce on The Clearout
 
So many more beautiful bass tones-too numerous to mention, but Stanley's tone on a song where he sings Hail, Space warrior, you have come a long way springs to mind.
Just my $0.02
 
George

Since Georgie's added bass tone to the thread, allow me to tip my hat to Phil Lesh for Mama Tried off Skeleton and Roses - my favorite bass tone of all time.  I've been known to listen that to song 3-4 times back-to-back just to marvel over that tone.  There's a quality to it that no one else gets, and I've never heard Phil  get as strongly as here.  I fear I lack the language to describe it adequately, but the word that comes to mind is bouncey.  I don't know how tone can be bouncey, but I guess that's why he's Phil Lesh and I'm not.
 
Peter