More » The largest of the free dating sites, POF boasts an (estimated) 23 million unique members using the site every month.
While owner Markus Frind has wiped the site of folks only looking for casual dating or an age-gap relationship, I've found this has only increased the incidence of folks lying about their age or intentions.
Still, it's a great site to get your feet wet in the online dating world, just to see what's out there and how the process works.
More » Zoosk hosts an estimated 11.5 million unique users a month, and it's easy to see why: the sign-up is quick and easy, there's little to no profile writing needed, and the search features prominently display photos.
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).