Lord of the Rings Soundtracks... Between 3 albums there is a wide variety of musical "mood".
Gladiator is simply excellent.
Dune (Dave Lynch's version), but avoid Tracks 10 and the last Track (to much Toto comes through...), and Children of Dune (Sci-Fi Channel's version)... Both are fairly grand and epic sounding, with Dune being a bit on the dark and gloomy side.
When dealing with "natives" and the like, I tend to pull out Micky Hart or Native American music.
Dark City has some excellently creepy stuff as well as a track or two that are very combative.
Hulk is actually a decent soundtrack, as are the X-Men soundtrack.
Star Trek has a good number of excellent tracks, but they are scattered across ten albums (Klingon War Anthom!), and same goes for Star Wars (Asteroid Field from Episode V), although both have heavily-recognized "themes" that can offset the mood being set by recognition/familiarity.
When fighting the "hordes" or some such, I tend to pull out the Slayer... Corrosion of Conformity's Echoes in the Well is an excellent mood-setter ("Listen to the battle cries of a race that knows it's dying..."), as are Judas Priest's Rocka Rolla and Rush's Bytor and the Snow Dog.
And this list will continue forever if I keep typing...