I use a cheap spiral bound scrapbook that I got a Michael's. I put a picture or two of the quilt (with the recepient if it is a gift) and sometimes a fabric sample. Then I write about the quilt-
-what inspired this quilt?
-did I find the fabric first and then a pattern to go with it, or the other way around?
-what pattern I used.
-anything special about the quilt or the reason I made it for that person
-the month and year when the quilt was started and finished (sometimes that is a LONG time in between :D )
-the size of the quilt
-any other detail info I want to include
When I feel like I never accomplish anything it is fun to go back and see all the quilts (wall hangings, lap quilts, etc) that I have finished. Since I have given so many away as gifts they are not around to remind me of what I have done.
I hope that some day when I am dead and gone my grandchildren or great grandchildren may like reading about their old Grammy and what inspired her!
It is a great idea to document your work. Good luck with whatever method works best for you.