My favorite is Liquid Tension Experiment 2.....basically Dream Theater with Tony Levin on bass and the Chapman Stick.

Oh, Derek Sherinian's solo album Black Utopia is awesome......probably the only time you'll ever hear Zakk Wylde and Yngwie Malmsteen playing a guitar solo duel, well, probably the only time you'll ever hear them play on the same album.
Some guitarist on this album: Zakk Wylde, Yngwie Malmsteen, Al Di Meola, Steve Lukather...that's all I can think of off the top of my head.