What's your favorite boss battle theme?

Probably a tie between Beelzebub from Nocturne and Pleather for Breakfast from NMH

One Winged Angel - Final Fantasy VII

How has no one mentioned Danger from Secret of Mana? Failures, the lot of you. :P

A close runner up would be Xagor's theme from Final Fantasy Legend III. Shame the version in the remake isn't as awesome...

Secret of Mana - Danger

I loved the music in the RPG Lost Odyssey. The below link is from the final boss, it is the extended version so the intro goes on for a minute then starts properly. Great bit of music to go with the fight.

Lost Odyssey: Final Boss Theme (EXTENDED)

Sonics (The old ones) from Sega Genesis/Mega Drive

Shining Force 2 final boss theme:

Zeon

Dark Souls - Gwyn, Lord of Cinder (can't forget the credit song) or Peace Walker - Zeke

Only this one comes up to mind:

Zone of the enders 2 - Bahram Fleet

Darksiders 2 - Guardian Boss Music

Persona 4 - I'll Face Myself

no the best song on that OST, but definitely some great music
Super Meat Boy - Dr. Fetus

http://www.youtube.com/watch?v=piylFkYIvuk

every boss battle cutscene from Xenoblade!they all had same song and that was awesome!

Final Fantasy VII - Those Who Fight Further.
Pretty sure that one only plays during boss fights

Undertale - "Heartache"
http://www.youtube.com/watch?v=XuHRujw1IOc

Errytime

I have so many favorites, but this one will always be in my top five.

For me it must be Jungle theme from Mercenary Kings.
It's just so awesome and gives you energy.I jump on my chair every time it pops up!

Game: Electronic Super Joy.
Boss: Wizard.
<3

Edit: I APPROVE OF YOUR CHOICES VERY MUCH.

http://www.youtube.com/watch?v=6CMTXyExkeI

Final Fantasy V - Gilgamesh

This from Contra

Mine is the music that cuts in on epic fights in Dark Messiah. It is dynamic so when you start a big fight (cyclops, dragon, etc) it just starts playing. Definitely gets the blood pumping!

One winged the angel - Final Fantasy VII

Boss: Sephirot

Chrono Trigger - Magus Battle

Dark Souls - pinwheel, not the best boss fight but the song is epic :D