Lazy Web Query: Wikis

OK. I've been using PBWorks for our work wiki. They incorporated folders to organize the various stuff, except that you can't nest the folders. It's just one level. Well, I need to be able to go a bit deeper than that. At least this is what I've told our treasurer we can do. It doesn't appear that Wikispaces have any foldering option.

Anyone out there have a pointer to a wiki that can?