Project Linus - http://www.projectlinus.org/
Project Linus is a national organization that has hundreds of chapters working with thousands of volunteers across the United States. With the help of volunteers, over three million blankets have been distributed to seriously ill or otherwise traumatized children since 1995. To help, contact the Project Linus chapter closest to you.
Quilts for Kids - http://www.quiltsforkids.org/about/
The founder of Quilts for Kids started out repurposing discarded fabric samples, turning them into quilts to comfort children dealing with life-threatening illnesses, those suffering from abuse and international orphans. You can help in their mission by requesting a quilt kit to be shipped to you.
Quilts from Caring Hands - http://www.quiltsfromcaringhands.com/
Quilts from Caring Hands volunteers make and distribute quilt for free to at-risk children in Oregon. You can help by donating a completed quilt or quilting supplies.
Relief Share - http://www.reliefshare.org/index.html
Relief Share provides all kinds of necessities to needy families. Check their "Urgent Needs" page to see how you can help.
Rosie’s Calico Cupboard Quilt Shop/Camp Reach For The Sky Project - http://www.rosiescalicocupboard.com/CR4TS2003Involvement.html
A group of people organized by Rosie's Calico Cupboard Quilt Shop in San Diego make quilts to be given to kids that attend Camp Reach for the Sky, a camp in San Diego for kids between 4 and 18 who are fighting cancer. There are many ways you can help, either by sending a completed quilt (twin size or larger), quilt blocks or quilt tops. They will take care of finishing any unfinished quilts. They also take donations of material, batting, and other quilting supplies. They especially need more long-arm quilters.
Sewing for Babies - http://www.sewingforbabies.com/default.htm
This is an Arizona organization that makes clothing for needy babies. They have monthly sewing meetings as well.
Stitch-a-Wish - http://www.threadsoflove.org/
Threads of Love is a Christian organization that has chapters in both the United States and Canada. They provide clothing, blankets and other handmade articles for premature and sick infants. Contact your local chapter to find out how you can help.
Tactile/Touch Quilt Project - http://www.seeitourway.org/Archives/2008/TactileQuilts.html
This project makes tactile objects for visually impaired and blind children to stimulate their sense of touch. They are looking for donations of materials as well.
Touching Little Lives - http://www.touchinglittlelives.org/
Newborn and preemie sized garments and other baby accessories are needed for Ohio's needy babies. You can help by joining in on work groups or making items.
Warm Hearts ~ Warm Babies - http://www.warmheartswarmbabies.org/
The volunteers of Warm Hearts sew, knit, crochet, and quilt for premature infants and babies in need. Items are donated to hospitals, crisis pregnancy centers, shelters, law enforcement and foster care agencies, WIC offices, and individuals across Colorado. They accept donations of handmade items as well.
Wrap Them in Love - http://www.wraptheminlove.org/
This foundation collects quilts and distributes them to children around the world.
I hope this list inspires you to put forth your valuable time and sewing skills helping others.