I'm not always a friend of charity drives in games, because I feel that sometimes these are just marketing tricks that help the game company more than the charity. Especially if not 100% of the money goes to charity. Why would I want to buy a virtual item for $10 of which half goes to charity instead of giving $5 or $10 directly to that charity? Having said that, player-run charity drives are obviously a different story.
The guild Sacred Fire is doing a 24-hour charity MMORPG marathon playing session on October 15th and is looking for your support, with 100% of the money going to the Children's Miracle Network Hospitals. So if you are willing to pledge $1 per hour for one of the participants, you can do that on this page. Looks like a worthy cause to me.