This is a very handy item to have if you have a few filters. It folds out (see next picture) and has pockets to store up to 8 filters. It is about 8 by 4 1/2 inches when folded up. It holds 8 filters. This one cost $8.50 and is well worth it, I am sure there are a lot of different ones out there, just look around.

Link to this one.
http://www.cameragear.com/filterwallets.asp