That quilt idea is so cute! We wear our letters a lot, so we have lots of t-shirts and sweatshirts and jackets, and when people go alum, they donate their old shirts (especially the ones we use for rush parties) to a box for the new members and they get to take what they want out of there. I got a ton of shirts that way, and I'll probably donate some of my old ones back for someone else.
Another thing I've heard of people doing with their old t-shirts is making throw pillows out of them. I thought that was cute too.