Let's face it, appearance determines a lot of matches online. If you're even more concerned about appearances than the average person, Beautiful People might be for you. To make an account on the site you must have your images "approved" by existing members. Basically, if you're into exclusive clubs determined solely on appearance, this is a great way to meet other people just like you.
But, if this sounds slightly horrifying, another site is probably a better choice.
On the other side of the coin, Ugly Schmucks is a website that matches people who aren't confident in their appearance with those who are more interested in personality than looks. The site states that it intends to help people fight the barriers that society puts on dating, and insists that "you can be very happy on an ugly date".