I keep mine in cel books in my dresser.  ^_^  
That way they don't get dusty and are quite 
protected.  However, it leaves less space for my 
clothes.  :D

I have a question- why do some of us still keep 
the cels we have, even though for many series, 
new cels seem few and far between?  Sentimental 
attachment, hate losing money, or are you still 
just as fond of the series and the art itself as 
you were when you bought the cels?