Cellfire is a great website where you can add coupons to your savings card (i.e. Harris Teeter VIC Card, Safeway Club Card, etc.) and it will automatically deduct those savings when you ring up. It's a very cool website and a great way to 'go paperless' in the coupon world.
Sign up here and you can start adding coupons today! Of course, this is free or else I wouldn't be telling you about it :).