Here are some links to some of my favorite dog supplies, information and resources.  I have had good results with all of these suppliers.

Pet Food Direct is a great research tool for hundreds of foods and an easy way to access or order diets that may not be in your area.  They also have a nice selection of supplies.

Sentinel guards against heartworms and fleas as well as adult roundworms, adult hookworms and whipworms.

Sentinel is a product that the Collie Health Foundation accepts for Collies even if they are genetically affected (2 copies of the) MDR1 gene.  
One of my Collies was on it until we could verify his skin issue was zinc deficiency and NOT sarcoptic mange mites.  (The conditions look identical).

1 800 Pet Supplies- Their search bar can help you find my favorites:
The strong, braided and economical  Adjustable Puppy Collar buckles anywhere along its length.  I have a 10 year old collar that is still in use!   And matching Rainbow Nylon Puppy Leads are available.   The Adj Choke Collar works well for my Dobes and Smooth Collies.  A largest selection of Dog Coats (that I have found) for our Dobes in the winter too!

Dog.com has plenty of pet supplies with links to their horse and garden supplies. Simalar products to 1 800 Pet Supplies but some prices are slightly different.