What types of encounters are you envisioning? For example, there are a number of great classical pieces/waltzes that would be appropriate as background music while the heroes are attending a formal ball.
Outside of that, I like a number of game soundtracks for their ability to convey mood/atmosphere. Most notably, pretty much anything by Jeremy Soule
(Elder Scrolls, Guild Wars, etc.) or Inon Zur
(Dragon Age, Prince of Persia, etc.) fills my fantastic music needs. If nothing from the two of them suits your fancy (which I'm guessing to be pretty unlikely), I can drop a few more names.