The most interesting one I have found is Cyndi's List. In case you don't know, Cyndi now has her own domain name as she was sponsored by a company which will now allow her to do more with her site. Her new address is http://www.CyndisList.com
EXTRA CREDIT: Even though you can find information on the net, I do believe it should be used more as a guide than a "take as word". What we have to realize is that most of this information has been entered by human hands which means it could contain typos or other errors. It's kind of like the game we used to play as children where we would start a line going and one would whisper into the first one's ear and then pass it along down the line. By the time it got to the end of the line, something totally different was said!
Also some of the information on family trees may have been put up there without checking it out (i.e. information received from Aunt Emma who is 99 years old who is not really able to recall the exact time and place but thinks it is this - and this information is put down as a fact.)
Therefore, if you find anything, just use it as a guide for possibly digging further or getting the record for this information.