Zoosk

I bet you've never heard of Zoosk before. And no, I didn't just make that word up, it's an actual web dating service that started in 2007 as an application on facebook. They have basic free membership but to vastly improve your possibility of matches you need to pay a monthly fee. They also have Zoosk coins that you can purchase virtual gifts with, make your profile more visible to browsers and receive special delivery confirmation. You were able to "unlock" conversations with other members using Zoosk coins as a basic member, but I found a review stating they've changed that policy and now the only way to "unlock" conversations is to become a premium member which costs 30 bucks a month.

This is probably the most versatile of all the web dating services because you can download the application on a number of different social networking sites and also mobile phones.