I just download a new application from the iPhone app store called Coupon Sherpa which defines itself as an "in-store coupon application for the iPhone."
You simply browse for a store or restaurant by category or check the alphabetical list for your favorites. Most coupons show up with barcodes that can be scanned in at the register when checking out. (Others lead you to the offer on the vendor's Web site.) As of this posting, there are 178 coupons in 111 stores in Coupon Sherpa, including many major retailers.
The app is only $1.99, but, in celebration of Earth Day, and to highlight one of Coupon Sherpa's goals "to reduce the amount of paper that is wasted by printing coupons", the application is free until this Friday, April 29. (But well-worth the cost of the app anytime!)
I cannot wait to try it out later today when I go shopping. It will be interesting to see how handing the iPhone to the cashier will go over, but I think they had better get used to it!