So many good things...
One of my favorites is a set of posters showing a panorama of each park's main throughfare and its icon. (MK's has Main Street and the castle, EPCOT's shows World Showcase and SSE, etc) They're about $25 each -- $100 for all of them. Of course, you can also buy them all framed up for about three gazillion dollars at the Art of Disney stores. They really take you back to the parks when you want to be there, but can't.
If you're looking for something a little cheaper, grab an extra map of each of the parks and put them away (don't even open them). Then, when you get back home, get them framed or mounted on styrofoam. Kind of unique, and rather cheap. There's even a place near where I live that will remove the creases/wrinkles/etc from stuff and mount it on styrofoam.