Surprise My Pet
Surprise My Pet is a subscription service for dogs. However, they are looking to add other pets as well. During sign-up, you are asked to specify the size of your dog (tiny, small, medium or large). Each month, they send 4-7 toys, treats, chews, and other goodies that's appropriate for your dog.
[9/9/2015 Update] Surprise My Pet has lowered all of their subscription prices significantly, but removed the 6-month option. This is reflected in the details below.
Monthly: $25.00 Per Month
3-Month: $23.00 Per Month
Annual: $19.00 Per Month