I use 
American Plas-Tech which takes both Paypal and 
regular CC.  The only drawback is that they have a 
$40 minimum order, which is a _lot_ of 
polypropylene bags.  (They also offer Mylar, which 
are considerably more expensive.)  

They're perfect if you want to split an order, or 
just to have enough cel bags to last a loooong 
time.

--Atiya