I like to go to the manufacturer's websites as much as possible. Their coupons are usually better than the ones on RP or Coupons.com. Betty Crocker, Nestle, ConAgra, etc. I just got $1 coupons for V8 Fusion by clicking on an ad that was in the margin of my aol mail.
One of the better data banks for online coupons is afullcup.com. I also like hotcouponworld.com. If there is a printable internet coupon out there for what you're looking for, the members on those two website will most likely have a link posted for you to use.