I'm REVIVING this topic back from the dead since between the LAST (2009) post and now (2010), Nier came out. =)
A few others I wanna add...
Chrono Cross - ending theme
Romancing SaGa - ending theme
Persona 3 (eugh, a few tracks, the engrish can really be a turn off when some parts are totally muddied up, I admire the effort though).
Kingdom Hearts II - I loved Passion, sounded unlike anything heard in gaming vocals.
Ar-Tonelico (a number of tracks, too many, and too many weird-named ones to list...Cosmoflips [great title] was great in the latest title though, as well as the opening)
Valkyrie Profile II - I loved the "epic Latin chanting
" in the final battle