wazamba com
By signing up you begin a free two week trial where you can play unlimited games for free. You are under no obligation to subscribe at the end of your trial. To continue playing after your trial, you can subscribe for justR$6.99 a month.
You can play it for free, but you can change the themes to special colors you must pay. It's very fun! It even teaches you how to play. I never knew how to play it until I read how to play Mahjong!