Ok Cupid This free dating site has exploded onto the scene and it offers a cool option.
They also have a blog about ways to use the dating site, and a recent post on what types of profile pictures work best is a great example of how they offer real advice based on actual usage by real people.
Craig's List Personals This used to be the the ultimate personals site, but now it's loaded with so much spam and fake ads that it's hardly worth it any more unless you're very patient.
Categories include romance, casual encounters and more.
If you're tired of just dating and want to cut straight to the chase, check out the adult dating sites instead.