For something a bit different from the other recommendations, you might try Devin Townsend, either Ocean Machine or Terria. Also, Scenes From A Memory by Dream Theater (or any of their other albums, but that's their best), Lateralus by Tool, V - The New Mythology Suite by Symphony X.
And to prove I'm not just a head-banger, how about the new Telarc recording of Tchaikovsky's 1812 Overture (maybe not the best performance ever, but they sure went all-out and it will give your sound system a serious workout).
