Check out
THIS THREAD.
This is a great list... I sent an email to at least six of them, and got samples back from every single one. I ended up going with Chicken Soup for the Puppy Lovers Soul because my puppy likes it and it's actually sold at a pet store near us. In the email be sure to tell them how old your dog is, and what breed, and they will all send you samples of whatever food they sell that is best for your pup.
Good luck!
Lauren & Nikko