Thanks for the recommendations.
I get what you guys are saying.
Maybe I should also state the purpose of the question: a friend of mine likes to build worlds, and so we decided to try to make an RPG together, me the mechanics and he'll do the setting.
I'm basically looking for resources that will give me an overview of possibilities (the sky's the limit, I know, but I'd like some inspiration as well as the pros and cons of each).