Where have you been looking, and what demographics are you after?
http://www.alexa.com/siteinfo/plentyoffish.com—huge, free, mostly 20s
http://www.alexa.com/siteinfo/match.com—huge, paid, mostly 30s
http://www.alexa.com/siteinfo/eharmony.com—huge, paid, marriage-oriented, mostly 40s
http://www.alexa.com/siteinfo/okcupid.com—not as huge, free, mostly 20s, smartest demographics of the major sites as far as I can tell
Where have you been looking, and what demographics are you after?
http://www.alexa.com/siteinfo/plentyoffish.com—huge, free, mostly 20s
http://www.alexa.com/siteinfo/match.com—huge, paid, mostly 30s
http://www.alexa.com/siteinfo/eharmony.com—huge, paid, marriage-oriented, mostly 40s
http://www.alexa.com/siteinfo/okcupid.com—not as huge, free, mostly 20s, smartest demographics of the major sites as far as I can tell