ItsYourTurn.com
In addition to American Checkers, ItsYourTurn.com offers International Draughts and numerous variants. This is a turn-based web site.
OnlyCheckers.com
As the name implies, OnlyCheckers.com is a site about Checkers. The online play options include American Checkers, along with Armenian, Brazilian, Russian and many more.
Games.com
Games.com does not have many versions of Checkers (just two, in fact: American Checkers and Casual Checkers, in which jumping is not mandatory). But it does tend to have a lot of players.
Yahoo! Games
Like Games.com, Yahoo! Games doesn't offer many versions of Checkers, but it does have plenty of human opponents.
Pogo.com
Pogo.com also tends to have a good number of potential opponents, although it only offers American Checkers for online play.
