Having said that, I've found a larger-than-average number of folks looking only for something casual here (likely due to the lack of time investment needed to join), and I've yet to hear of any successful relationships come out of the site (where readers tell me they've met The One, or something equally special, on the site).
More » I freely admit that I'm biased when it comes to Ok Cupid, as it's taken my top spot on my Best Dating Site list for years now.
With an (estimated) 35 million unique monthly users, has the largest active membership of all the dating sites out there - and for good reason, however with some caveats: it's geared more towards folks looking for long term relationships, you'll want to carefully craft your profile to focus on such, and make sure you carefully review all emails for potential romance scams, as Match seems to attract more than their fair share of mysterious strangers trapped in Nigeria.
Considered to be the first successful free dating site model on the Internet, Owner, Markus Friend, still runs the organization by himself even though his user base outnumbers most of the pay-per-use websites around the world.
The amount of people using Plenty of Fish (which includes heavily-trafficked forums, compatibility questionnaires and the very popular Who's Seen Me button) is astronomical in its sheer ability to connect with users around the globe looking for friendship, love, and anything else in between.
The only 100% free dating site on this list, Date Hookup offers pretty much anyone a place to chat, meet, and hopefully connect with other singles.
While I found the site cluttered and confusing to use, they're obviously doing something right with three million unique members visiting every month.