Did some searching - I have used grocery IQ (free app)
Grocery iQ for iPhone, iPod touch, and iPad on the iTunes App Store and think it's pretty good, although I haven't taken advantage of all its capabiities. I also have grocery gadget lite (the free version of a $4.99 app
Grocery Gadget - Shopping List for iPhone, iPod touch, and iPad on the iTunes App Store) but of course the lite version has limitations. Think I would fully test IQ before I pay for the gadget version.
I really like the option to set up multiple stores and keep a separate shopping list for each. And there is a coupon feature that I haven't tried yet -- but it looks pretty interesting.
I'd like to hear what you end up trying and what you think of it.