I order mainly from wag.com, naturalk9supplies.com and petfooddirect.com.
I ALWAYS go to retailmenot.com and check for online codes. Often I find better ones there than I get in email or on Facebook. I go there for ALL online shopping codes.
I just ordered 4 bags of ZP and some S&C from naturalK9supplies. Their discount code made the order less than wag.com even though I met wag's free ship hurdle. So, I will open two windows, place items in both carts, use codes and complete order with least expensive place.
If I order by 10 p.m., wag.com delivers still the next day so I choose them most often for that reason.