I've never been on one, but it's usually 30 bucks a month. The online one that I've seen work the best is "Match.com" My friend went on it and the outcome was good. Three girls! He's not dating them anymore, but he did get to.....you know.
His profile is still up there right now. Its been like 2 months for him.
However my other friend got nothing. Alot of people are on that from all over the United States. He showed me how it worked and I was pretty impressed.