I second the flat rate box idea but you can order them online so you don't even have to leave your house!
I for one would be interested as I posted a request for pillowcases and lap quilts for people with AIDS back in Novemeber and two members contacted me but so far nobody has sent in any items to the organization. They could use fabric , so that quilters could turn them into quilts. I would be willing to pay the postage on behalf of the group.
I am sure other charity quilters would do the same.