I've done a bit of research and have come up with a list of organizations in need of handmade items for the person(s) they serve. Have a look through this list. I'm sure you'll find one or two that might help you decide to get involved, too!
Project Linus volunteers, also called, Blanketeers, make blankets for kids who are seriously ill. These handmade blankets can be quilts, crocheted, knitted, or even made tied fleece. There are Project Linus chapters in every state.
ConKerr Cancer accepts handmade pillowcases. These cases are then given to kids who are battling cancer. There are ConKerr Cancer chapter nationwide.
The Ships Project is an organization supporting America's military troops. They accept handmade knitted socks, knitted or crocheted slippers and hats.
Soldiers' Angels Sewing Team also helps out America's military persons. There are multiple ways to help this organization, but the Sewing Team works to make blankets, sand and "cool" scarves as well as pillowcases.
Binky Patrol is a national organization of volunteers who make and distribute handmade blankets to kids currently in foster care, children born HIV +, infected with AIDS, abused, or chronically or terminally ill. The blankets can be sewn, crocheted or knitted.
Threads of Compassion is a group of sexual violence survivors based in Chicago. They support "new" victims by giving them handmade (knit or crochet) scarves when they enter a hospital for emergency treatment.
Compassionate Creations is a Massachusetts chapter of Threads of Compassion. This group also helps victims of domestic violence and accepts lap squares (18" to 30" square) and wristbands as well as knit or crocheted scarves.
Carewear volunteers sew, knit, or crochet handmade baby items for hospitals. There is a huge list of links and patterns on theCarewear website.
Wrap Them in Love is an organization that collects and distributes donated quilts to kids around the world. This group is based in Washington.
The Shawl Ministry website has a lot of information (and patterns) about joining and or starting your own Shawl Ministry.
NEW:
One Warm Coat is partnering with Redheart yarns to donate knit or crocheted scarves as well as new or gently used coats to those in need.
Skeinz, a yarn company in New Zealand, is requesting knitted "P.J.s" for penguins. These P.J.s help to prevent the penguins from preening their feathers and injesting toxic oil. There are specifications for the penguin jumpers and additional information regarding the request on the Skeinz website.