I've put together a brief list that mentions at least some of the many live streams that are going on today for Extra Life. Extra Life is an annual gaming marathon that happens in October. The goal is to raise donations for sick children by gaming for at least 24 hours straight. This year, the marathons are taking place on October 20 (today) and there are plenty of streams to watch or way to participate it. Over 15,000 gamers are participating but I've tried to list some of the large ones below:
Infinity Ward's Call of Duty's team
The MMO RIFT is having their Extra Life weekend right now. You can get a title if you participate.
To find more streams, you can browse twitch.tv for individual player streams and more. Extra Life also has a directory where participants can leave their live stream addresses.
Basically, if you like the live stream you’re watching, find out how you can donate the money to that team (you should be able to do a search on the Extra Life site for the team—it's on the main site on the upper right) and sometimes you can even receive prizes for donating. Some are in-game prizes from developers but some are physical.
All in all, it's not that far into Saturday and already thousands of dollars have been raised to help save and improve sick children's lives.
