Depends on what tone you plan to give it. The Guy Ritchie/Robert Downey Jr. Sherlock Holmes movies work pretty well for typical adventure-goofy games, though it might be too iconic. If you plan to go super serious, grab something off the Koyaanisqatsi soundtrack. "Arcanum: Of Steamworks and Magick Obscura" has some nice tracks that fade into the background.
Solomon Kane feels Zeitgeisty. With muskets and magic and some fun sword fights.
Three Musketeers is also a good one and feels time appropriate.
The Patriot is good as well. Could inspire Yerasol Veterans for the last war.
Now for a weird one, Les Miserables. But mostly for the architecture and uniforms. Javert pretty much wears what i picture the official RHC uniform, although i picture for most groups they wont wear official uniforms during most of the adventures.
Everything that RangerWickett just said mostly
Our version of Zeitgeist might be a little more straight-faced than most peoples, but my primary inspiration is The Wire, especially for the first act. I like how the show is centered on a city and the interactions of its various factions, all of whom are at least a little bit dirty, and none of whom can easily be categorized as "good" or "evil."