Sake, Bugs, and Angels - Not just a good info site, this page also has probably the most thriving OMG fan community out there.
Open Your Mind This OMG TV fansite is the place to go for detailed comparisons between the TV series and the manga.
Megami-sama.net This domain features a scan gallery of recent images for the new TV Anime, a shrine to the demon Mara, and a weekly updated media page with clips from the latest episodes.
Nekomi Kodai(currently down) My friend Ed's site, which has a lot of good info, but probably won't be updated in the near future, since Ed is a medical student now, and not likely to have a lot of time. Still worth a look.