Under A Glass Moon solo is amazing but I don´t find it that hard. Another amazing solos by Petrucci are Erotomania (the last one), Voices (lot of cool penta stuff mixed with some wicked stuff as well), Lie (the last one is amazing. If you want to learn that one be sure to pick all those 16-notes at the end part), Fatal Tragedy (probably the best and absolutly the hardest one for me) and Home (I just love solos with Phyrgian scale and for that matter try Metallicas Wherever I May Roam).

Another cool stuff is Vai´s For The Love Of Good, Surfing With Alien and Summer Song by Satch, Far Beyond The Sun is the best song I´ve heard with Yngwie, there´s lot cool stuf with Racer X and Rhoads/Lee/Wylde combination is one of worlds best. Another amazing stuff that I can´t play ´cause I only got 22 frets on my guitar is Serrana by Jason Becker.

But advanced solos are not always the best ones. Just listen to Dire Straits, Guns N´ Roses, Bon Jovi and you´ll fin tones of good stuff. Hotel California solo by eagels is very very nice and yet very very simple. But of course, it can be hard somtimes to get the right feelin´.