As far as the virtuoso players with solo albums go, the most technical ones I've heard are:
Vinnie Moore - the guy plays very musical stuff with a mix of neo-classical and his own style. His sweep picking is mind boggling becuase of the shapes he uses and the unbelievable speed and fluidity. A good track to get an idea of his techincal stuff in 'Defying Gravity'. Free MP3 samples are on his website too.
Rusty Cooley - not the most musical shredder out there but the guy plays impossibly difficult runs at very wierd meters (7ths and 15th) at a speed that is unparalleled. Didn't think too much of the Underworld project but his solo album is worth a listen. As I said, it's no tht most musical, kind of like a twisted circus act/car crash that gets you interested at all the wrong levels.
Shawn Laine - simply the baddest gutarist ever. Vai, Petrucci, Malmsteen have all cited him as a true master of the instrument. He played loads of very mellow stuff too but the first time I heard him break out at maximum speed and difficulty I actually couldnt believe what I was hearing. Good thing about him is its not all speed and difficulty, he plays a bit of everything so if you like guitar then you should like him.
Loads of good mentions in previous posts, have a feeling I'll be joining the queue at Amazon!