my favorite is designsbyjuju.com I like it because they are cute. I do a lot of childrens items. her prices will say 20 per set, but there are always offers that bring them down to 4 or 5 per set.
she has a full page of freebees to try.
Many great designers and sales at oregonpatchworks.com . this is a mall type of place with many individual "stores"
you can pay with paypal at all of them. most have instand download.