Adult Friend Finder
If you are really serious about hooking up with a girl and you are looking to get the most bang for your buck I would have to say Adult Friend Finders is the way to go.
When it comes to dating, casual sex, or meeting couples for threesomes they have a massive amount of profiles from all over the world, and from experience I know that they have the least amount of fake profiles because Mr.Jerk had a membership at Adult Friend Finders for years.
Most profiles have nude pictures (over 98,000,000 hot members photos site wide) and videos attached to them so it's easy to pick the right chick that you want to hook up with.
They have lots of other features as well including live amateur webcams, live chat and dating forums, one of the biggest attractions that has the most profiles is people that are into the swinging scene, also they have sex group meets probably better know as group fucks or orgies where they get together at a hosts house and fuck and suck the night away with each others wive's, girlfriends and husbands, most of these groups you have to wait to get approved to join their private groups but you will find open groups as well and it's a matter of finding one that is local to your area.