I looked at GirlfriendCircles once, but there were about 3 people listed for my area If you do sign up for one of these, please report back!

I have tried Meetup and have not had a great experience, I think because I am in a town of less than 100k. Craigslist also didn't work for me - I got a lot of perverted emails, some of which were very funny, but still not really what I was looking for.

I like local interest Facebook and Linkedin groups-- you can get a good feel for the various people before meeting them. I haven't gone to a Tweetup, but I bet that's similar to the other two. And free is good!

I am a huge fan of classes as a way to meet people. I've also been joining some interest based offline groups. I was telling my boyfriend tonight that I think we should start becoming regulars at some bars - I've never had so many friends as I did when I bar hopped (and I never drank!).