OkCupid

A totally free dating social network 

It's a totally free matching service. It's also extremely accurate, as long as (a) you're honest, and (b) you know what you want. We don't claim to evaluate you perfectly, but we do claim to find someone who claims to fulfill your claimed requirements, exactly. We firmly believe that most matching sites are just personals services; their "matching" systems are nonexistent or overly subjective.

While we have a small team here, we all take math (and all that math implies) very seriously. OkCupid is a fun project for us for a variety of reasons, only one of which is the actual content. We aim to be the best matching service on every front: superior technology, better math, better psychology. And of course, it's free, unlike all the others. 

Website:

http://www.okcupid.com/