Open-ended (on both ends) 11 x 14 sleeves.  These 
are great for me since they perfectly fit in 11 x 
14 itoya books and don't have sticky flaps (which 
can stick to cels and sketches if you're not 
careful).

http://www.iconusa.com/Onlinestore/sleeving.html

Product #S19050

Just bought 100 more of these sleeves.  They are 
also useful for making custom bags for odd cel 
sizes (i.e. cut them up and tape the pieces 
together).