I recently came across some things by Nicolo Paganini (sp?), a classical violinist and I've thoroughly enjoyed challenging myself by learning some parts of his pieces. Of course, some are way above my skill level.

Can anyone suggest more music like this that will give me a challenge?
Well naturally, I recommend Paganini. Even if you play one of his caprices twice as slow, it's still an accomplishment. Try some Mozart, Vivaldi, Bach, and Chopin. Some of that is Piano based music, but listen to it, and get a feel for classical music in genaral, it's good stuff.

There's a video called "Guitars from Mars". It's by Paul Gilbert. He explains classical pieces played on electric guitar and gives lots of examples.
not sure if its classical, its more flamenco but anyways, listen to steve stevens, hes the guitarist from billy idol, hes amazing, listen to his solo albums like flamenco a go go and memory crash, very good pieces.
Thank you very much one vision, and I have to say that I've always found the harmonic minor scale to be my favorite as well.
You can ruin this song like every other metal guitarist: http://www.youtube.com/watch?v=bWx_GyTLGmQ

Winter > Summer!! Figure it out people!

(I've ruined it too, so i have no room to talk)
“Science cannot solve the ultimate mystery of nature. And that is because, in the last analysis, we ourselves are part of nature and therefore part of the mystery that we are trying to solve.”

-Max Planck

All of those "Free guitar ebooks" are like 9kb....much too small... i scanned it and they dont have viruses but somethings not right with them....