Pretty much every theme except the Tolkien-inspired medieval fantasy really. I guess there's quite a lot of Star Wars inspired sci-fi at this point too.

I like the wild west suggestion though.
The african-inspired thing has been used in quite a few games actually. Hunter-gatherer african tribes are a fairly common area theme in some games (I'm thinking of that village in FF12 for example of the people wearing masks). When you do that sort of thing nowadays though you often get accused of racist stereotyping.