I played Metal gear 4 and Nier...and I guess you could say Nier had some rocking music but I don't know how I feel about Metal Gear. Don't remember anything fist pumping there... Just some sappy melodic stuff.

This has always been my favorite:

http://www.youtube.com/watch?v=mQU7ml26JVM

I think the issue is there is just a lot more going on in games now days. You used to pull up on a boss battle, and they would pan the camera around slowly as the characters had a stare down, because that was about all they could do. Then the battle starts and they play the same basic cords over and over. Now the music is just to over the top, the characters are taunting each other, and there is all kinds of action going on.

However, in all honesty, I can not think of any other boss battle than that DKC one as far as music goes.

Heh, I beat Chrono Trigger over 10 years ago and I still remember the game and this music. I beat DmC 4 weeks ago and I don't remember much of the levels and none of the music.

Its either cause of lackluster music or my age and long term memory loss lol...

Here's a much more recent game with a good boss theme: http://www.youtube.com/watch?v=Xa7p1MQNeW4

I coudnt remember dark souls music because i rarely heard it.

A discussion about boss battle music just isn't right without Shadow of the Colossus.  The entire soundtrack is amazing!  Here is one track:

Oh, and basically all of KH3D's (and most KH games) boss music are good.
example http://www.youtube.com/watch?v=rgEGYgYfDls

I'm partial to this.

I think Flow, Flower, and Journey are the best use of music in games that I have played this gen. Even though I could not even think of a single cord, it was great while playing, and really made the experience.

Spec Ops The Line had No Where To Run while trapped in a building on the way to the boss, that was good.

The God of War games have amazing soundtrack when going against bosses, actually always lol. Play some RPG's i would say then ;)