petsupplies.com - 25% off entire order, $4.99 shipping, $100 giftcard for $90
Just stumbled upon this. Haven't bought from them before, but prices seem fair enough? Be sure to compare prices with other places though (as bitFUUL pointed out below, places like bigalsonline could be much cheaper)!
Yes, there is. Once you click the link to their site, a window pops up with the code. Though I think the code might be activated automatically either way and then the prices on the site reflect it. In any case, here's a code you can try that popped up for me: 7F5E0H1OXY