Amazon. I could have gotten the Pampers Baby Dry size 4 for maybe $0.50 cheaper, but we like our Cruisers.
I used stackable coupons from Parents and Parenting magazines to get my diapers for $0.019 each ($0.10 each is my stock up price!). Amazon also has coupons that I was able to take advantage of. Thanks to the heads up Jeana gave me. Read her post here to do this yourself! I couldn't explain it better myself and didn't want to steal her thunder. :)