I had to share this, because lately I've been having an amazing amount of luck on this site. GenForum is a forum run by Genealogy.com. It has subforums for seemingly ever surname, as well as for countries (and every U.S. state), and a bunch of general genealogy topics.
There must be a whole lot of genealogy angels on that site, because I've posted questions twice, and both times I've received an answer within a day or two, solving a problem that I've been working on for months. So if you've got a brick wall ancestor, I highly recommend you post your question on the relevant surname forum, and on the relevant country forum (the country forums tend to be more active and I've had more luck there). Post everything you know about the ancestor and immediate family, and you'll be amazed what people will find for you.
And of course, if you're a skilled genealogist, I recommend you spend some time reading people's questions on the forums, and hopefully helping people out. It would be a great way to give back to the community.