Really fun to make because you get to make it completely your own! You end up with a collage that represents your style, or the style of the room it's going into.
Look through magazines, newspapers, etc. (look at the list up there for a whole mess of stuff you could use) and cut out whatever catches your eye! Use pretty much anything that looks nice and is somewhat flat and glue it down! :P
Other tips: Stencil letters onto a picture and cut them out to spell something. If you don't get what I mean check out this project:
Kusudama flowers artwork using old magazines