I use a system at Light Impressions for the bulk 
of my collection. I like to keep my cels 
vertically stored, so this system works great. It 
is an acid free binder which has cotton paper 
inserts covered in polypropylene. All you do is 
mount the cel(while in a cel bag) onto the paper 
and thats it. I use 3' mounting corners to give 
the cel some wiggle room and prevent warping. The 
set also comes with a slipcase to keep dust off 
of your collection and light as well. The whole 
deal costs about $75 and it will hold 35 cels. 
Now, I don't keep all of my cels in these 
binders, just the ones that I know that I will 
not be getting rid of any time soon. The rest are 
kept in Itoya art portfolios. You can get this 
binder setup by going to Light Impressions.