The first thing I thought of when I saw this thread was "
Kakusei" (Awakening) and "
Chikyuu Kyoumei" (Earth Resonance) from Chikyuu Shoujo Arjuna. The BGM is of course by Yoko Kanno... But I remember I genuinely had my breath taken away when those songs were used in battle scenes and I couldn't get them out of my head until I finally got a copy of the songs and could play them to my heart's extent. Great choreography + great music = happy me.
Then, of course, there's "
Innocence", "
Time Limit!!" and "
The spirit of FRAMENCO" (no, not Flamenco) from Melody of Oblivion, by Hijiri Kuwano. The anime wasn't all thaaat good after all but one of my most favourite things about it was the soundtrack, and I can still remember being so excited about the episode with Bocca and the bullfighting - I think they used the latter piece, and it was just perfect. I can't think of MoO without thinking of the soundtrack, and when I hear these tracks I sometimes find myself imagining up battle sequences to them.
There's also a good one by Yoshikazu Suo, "Phrygian Koko", except I can't remember where it was used.
I also liked the music from Bakumatsu Kikansetsu Irohanihoheto composed by Hideyuki Fukasawa, but with relevance to this thread it would definitely be "
Tsurugi no Sadame". I can't even remember which part of the show it was in exactly apart from it being in the second half or so, but I remember there was a water battle and confrontation with the Head and this music was used. I love the piano crescendo especially.
And I guess this is going to be terribly cliche, but I really did like "
Mezame" from the Mai-Hime soundtrack by Yuki Kajiura. For quite some time whenever I thought of "battle scene" I'd think of this song straight away... and then feel on the top of the world. Now, though, it doesn't have nearly the same effect. Speaking of Yuki Kajiura I'm tempted to mention "nowhere" from Madlax but I keep laughing when I hear the song, which probably isn't the intended effect...
Another one is "Shangri-La" from the Noein soundtrack by Hikaru Nanase - to be honest it's kind of overwhelming and a bit too over-the-top, but I'll be darned if I'll
ever forget the absolutely amazing battle sequences from episodes 1 and 12 and so on...
But for a long-time irreplaceable favourite, I'd have to say the
Rurouni Kenshin battle themes - I just can't remember the track names now because I don't have the soundtrack with me anymore, but one that keeps replaying in my head is one which starts with those picked strings... I almost feel excited just thinking about it
