The great thing about the Harry Potter mega-sites (i.e. the TLC, Mugglenet, Lexicon trinity) is that they're never-ending. No matter how many times you visit, there's always something you didn't notice before.
For example, today I was scanning the headlines at Mugglenet when I saw a link on the left to the "Plot Thickens Discussion Forum". I knew that the creators of Mugglenet had a book coming out discussing theories for Book 7, but I hadn't noticed the accompanying discussion forum.
It's a treasure trove! I generally skim a lot of the discussion--generally it's the same old subjects and same old theories being rehashed ad nauseum--but there were really some original ideas and topics of discussion. I especially liked the section regarding Lily Potter, and I think some of the guesses made there aren't far off.
Very grown-up writting (as opposed to the all smalls, no punctuation stuff that makes me nuts) and well-supported theories (as opposed to just stuff people are pulling from nowhere)--a very plesant place to while away a few hours.