I have three -

Shoebuy - free shipping, free returns, no tax, 10% off plus 10% if you buy again within 60 days, and I usually buy when there is another % off, and 10% SR credit!

1-800-PETMEDS - $7 SR credit with purchase of $40 - free shipping.

Drugstore.com - no tax, free shipping when you spend over $50 (which I always do), 5%SR credit and 5% drugstore credit.

I just could choose just one!!