JKRowling.com -- This is JKR's official website. It's done all in "flash" and has lots of goodies to find. It works best if you have high-speed, but you can certainly get around in it in dial-up.
The Lexicon -- It really doesn't need any more name than that...it's THE Lexicon. Here you can find detailed information about the Harry Potter books, including characters, spells, theories, myths, FAQ's, real-time time lines, etc etc etc. It goes on for days. Really useful.
