Alex Lifeson, eh?
#1 on my list too. If you're talking a top list then Eddie Van Halen and Jimi Hendrix are up there too. Hendrix is all the more impressive since he played by ear and didn't really formally learn to read music or the underlying theory before learning to demolish guitars musically. Eddie is on there because he's amazing and had such a distinctive sound you could always tell when a Halen song was on.
So, so many good ones.