I just signed up for shoprunner - I have been told it is a great way to save on shipping, so let's find out :)
PetSmart, Babies R Us, Toys R Us, and many others are included in the list of ship for free & return for free!

There is a members benefit section that gives addition discounts.

& another bonus??  Yup - you can use this in combination with ebates.

It's worth checking out and seeing if it will work for you.