Phantasy Star IV: Laughter
Shining Force: Darksol (extra goodness for those who've played Shining in the Darkness to completion)
Digital Devil Saga: Hari-Hara 1&2, Brahman
Nocturne: Dante Battle
War of Genesis: The Devil's Rhapsody

Anything that has an aggressive pace, good instrumentation, and a nice, dark sound (by which I mean a song that's definitely for the villain and not for the hero) is generally enough to win me over. However, there was one "heroic" battle theme that made my jaw drop.

Wild Arms 2nd Ignition: Battle with Lord Blazer.

Main theme rearrange comin liek WUT. Short and repetitive as is Naruke's style, but still fucking amazing.