Uhhh...this one here is very good.
Your sig says you have a 911, so are you looking for an FAQ on these cars? There's an excellent FAQ sheet, if you want:
http://www.connact.com/~kgross/FAQ/944faq.html
Clark's Garage is great if you only want 944/51 info, and tend to stay away from things like OT. I'm not knocking it at all though, it's a very resourceful site with great people and info. Also has the Garage Shop Manual, which is very helpful and accurate. All 944 guys, even those with a factory manual, will use it at some point.
Rennlist is another very good forum, but full membership is $18 (I think). Some will look down on you if you post too much there without paying.
All 3 sites are useful and frequented by guys who know these cars.