Random links I think you should visit:
Operation Christmas Child - Fill a shoebox with gifts for a child who may not otherwise get any!
FreeRice - Improve your vocabulary while helping donate rice at no cost to you!
The Literacy Site and its affiliates - Help donate money to worthy causes by just clicking a button once a day.
Project Download (which has an LJ community
projectdownload) - Download a file once a day to help Erin, who suffers from two neurological disorders, pay for the brain surgeries she needs. As with the above two links, the only cost to you is your time.
holiday_wishes - Spread the holiday cheer by granting people's wishes and posting your own. I'm a maintainer of the community (and participated last year as well), and I think that it's a wonderful way for people to connect. Not everyone's intentions are altogether altruistic, but overall the spirit of the community is very friendly and giving. (My wishlist is
here, if someone wants to grant one of my wishes! ;-) )
YA Fantasy Readers - A Yahoo! group I set up awhile ago that really doesn't have anyone there yet. It's meant to discuss - what else? - YA fantasy, and it's open to anyone, teen or not (after all, I'm barely a teen myself now!).