If you're on MTGO check out the Free Events via PDCMagic and Gatherling.
Other games you should try:DC Universe Online - action-based MMO. Free to play. Surprisingly well-designed combat and classes.
Planetside 2 - Free to play MMO-meets-FPS and the first shooter I've liked in ages.Simunomics - Free-to-play economy simulation game.
The stingrays, I assure you, are much more pleasant.
...I want to go to there.