Eric,
I really like the idea of a bound campaign journal but I would make some copies of the maps you used and put them in a really nice folder. Also you could use the picture idea, have everyone sign the picture and slide it in the front of the folder, you know one of those folders with the clear outer window.
What I've done in the past, although I paint miniatures, is give them a really nice painted miniature of their character and a new PHB with the whole group sigining inside the front cover.
But remember, you've already given them the best gift of all, the memories of a great campaign....
Hope this helps Eric,