I use 12x12" Pioneer scrapbooks for all my 
regular sized cels.  They are acid free and 
archival safe.  The cardboard inserts are a bit 
thicker than the ones in Itoya books so they 
support the cel better when turning pages.  They 
have thick hard covers so you can stand them 
upright on a shelf.  And, you can also buy 
additional insert pages to store even more cels 
per book.  I think they're great.

I buy these scrapbooks at a nearby crafts store 
(Hobby Lobby), but you can order them online 
also.  Here is a website that sells them - I've 
never bought from this site but it shows some 
information about these books:

http://www.archivalusa.com/k-mb-10p.html

Hope this helps!!
~Luna-Art >^.^<