I have a cool framing solution- I bought some 
document frames which are basically black 
plastic? boards with a sheet of glass which 
attaches with screws drilled through the board 
and glass, and has nuts which secure them.
Thus, the cel gets plenty of "breathing" room, 
and I leave them in the cel bags, so no worries 
about acid contact.  Plus, they are easy to 
switch with other cels, and I rotate to different 
ones every few months.  I have the frames in a 
deep bookshelf, with no exposure to sunlight (or 
direct flourescent, though I'll keep an eye on 
that.)  ^_^