My own experience is pretty similar to everyone else. I've been working on a setting here on the boards for about 6 months now, and it's intended to be a blend of many real-world cultures. For that reason, I've done a lot of Wikipedia'ing (and rabbit trailing from there) to find information that's concise enough to remain interesting to the casual reader, and juicy enough to entice gameplay.

Beyond making copies of real cultures, though, I'm interested in making this world my own. To that end, I head to art galleries and museums every few months (which may or may not be an option for you, depending on where you live) and see what takes my fancy. A recent--though not too relevant--example of this cherry-picking is a documentary I watched last night on Hawaii's geological, biological, and anthropological history. Between humpback whales, plovers, and the island's early polynesian settlers, I managed to get a lot of interesting ideas for a culture in my setting that's based primarily on medieval French and ancient Hebrew culture.

At every step, the important thing to remember is that you can get inspiration from seemingly unlikely places, and a little imagination will help you tweak your findings to the point that they seem unique enough to be original. Happy world building!