I spent all weekend in Columbus at a genealogy workshop (for librarians), hence this post! Michael posted a link to a site a while ago, but I thought I'd include another one!
This genealogy site is part of a larger on royal and noble genealogies if you are interested in more on this topic. This is actually a web version of a book by Funk and Wagnell. There is some interesting information here, but it really only deals with the Presidents and their immediate families. Anyway, it can make for some fun browsing! What I found the most interesting was seeing the parents and siblings - at least what information was presented.