I would first check with guilds, LQSs, hospitals and nursing homes in your area. If you do something locally, you don't have the hassle and added expense of postage.
Some national charity quilting can be done for Quilts of Valor or Project Linus.
There are other charities that request a bit less time by making bags, such as Sadie's dream for a Cure and Beads of Courage.
Finally, here's a link to the Requests area of this board:
http://www.quiltingboard.com/sitemap/f-25.html