Such a difficult question, there are so many great tones out there. Some of my favorites -
Randy Rhoads - Flying High Again. That first chord just comes out and hits you in the face. It's totally searing. Great song, killer tone.
SRV - Little Wing. The cleans are so crystal clear when he rolls back on the volume, but when the guitar is wide open it has this really lovely, warm tube sound coupled with his amazing playing on that track.
David Gilmour - Time. I really like his tone in this solo, sounds violin-like at times.
Zakk Wylde - No More Tears. Killer rhythm and lead tone, and those pinch harmonics in the verse really jump out at you. His tone nowadays has a little too much going on for me, I much preferred his tone on this song/album.
Jimmy Page - Since I've Been Loving You. The lead tone is so small, it sounds like it's coming from a 3" speaker but it still kills and fits the song perfectly.
Neil Young - Hey Hey, My My (Into the Black). The absolute heaviest, most distorted tone I've ever heard. Always on the edge of feedback or the amp exploding. The first time I heard this song, it totally took my head off.
Billy Gibbons - Just Got Paid. One of my favorite intro riffs of all time. Real greasy, bluesy tone on his intro. Come to think of it, anything with Billy Gibbons is pretty much guaranteed to have superb tone.
Jake E. Lee - Shot In the Dark. I really like his lead tone on this song. Plus, the fills he plays during the chorus are really complimented by his rhythm tone.
Norman Greenbaum - Spirit in the Sky. I think this is quintessential fuzz tone.
And many, many more.