I take pictures of each one. I keep a journal with all the info (name, person receiving it, date finished, pattern used, machine quilting used, and yardage of each fabric). I, also, keep a 2 inch piece of each fabric in the quilt. I usually glue them on a piece of manilla folder. I know a bit excessive, but when I first started quilting someone (I can't remember who) told me to keep a record. This is how she said to do it. I keep everything in a 3 ring binder in sheet protectors. It is a very good reference when needed.
And for the baby quilts I do, I always print a picture and some info on it kinda like a postcard. The parents put it in their baby book or scrapbook.