Here are some companies I've requested coupons from lately and had some success:
These were the coupons I received just last week :)
Proctor & Gamble, Organic Meadow yogurt and Clover Leaf tuna
Mrs.January has an excellent list of more companies you can try contacting for coupons, including Colgate, Barbara's, Tetley, Eden's Organics, Chapmans and more!
Click here for her list.