I just stumbled upon Tail Waggin' Celebrations, which is an actual party supply store for dogs.
If you want to throw your dog a party, this is your one-stop shop. They've got invitations, dog party hats, cakes and treats.
They've even got supplies for cat parties too.
If anyone throws a party for your dog or cat, I'd love to feature it on our homepage in our Party of the Day and blog about it.