I really like the Aquarium Pharmaceutical liquid test kits. They're easy to use and read, reasonably accurate, and not too expensive.
For food, I buy Ocean Nutrition and Hikari. I win alot of Wardley foods in raffles, and the fish seem to like them just as much too. I think variety is more important than brand where food is concerned. Have a variety of fish-based and veggie-based foods, and try to switch every day between dry foods (flake, crumble, pellet, wafer), live food, frozen foods, and fresh veggies.
I like Tetra Aquasafe, but I've used other brand declorinators just as well.
Lee Aquarium Products, Hagen, and Aquarium Pharmaceuticals make reasonably priced, high quality accessories (isolator tanks, air pump stuff, nets, algae scrapers, etc).