A rather fantabulous site that allows you to play various asynchronous games against other users on the site. You can have many games going at once and there are tournaments that can be joined. The games that can be played are:
My nick on this site is dizzyboy if you want to invite me to lose against you in stack4 :-)
itsyourturn.com is paid for by banner ad clicks. If you click on 3 ad banners a day, you get a little symbol by your name, showing you as a "friend of the site" which imho is a cool way to encourage banner clicks.