Obvious ones are Eddie Van Halen, Steve Vai, Joe Satriani...I'll throw in Neal Schon as well, anyone who can play with Carlos Santana as a teenager has got to be included.
But one that people may scoff at is John Mayer...whether you like his music or not, dude can shred on guitar.
Oh and Brad Paisley...another guy you wouldn't expect to be able to shred.
But maybe one of the all time best that nobody really talks about was Prince. Watch his performance of "While My Guitar Gentle Weeps" at the Rock and Roll Hall of Fame induction of George Harrison. Amazing.