+1 for Our Groceries. This is one of the most useful, time-saving apps I have.
I researched others mentioned above, but chose Our Groceries. Things we love & additional uses:
1) My wife & I can stay synced (even while tackling the same store from different ends).
2) Easy PC/Mac (as well as phone) editing on the OurGroceries website. You can even copy & paste text from existing lists. (Just use the "import" blank field).
3) Packing list & To Do list capable.
4) Crossed-off items remain visible (in a strike-through font) at the bottom of your list and can be restored to the list by simply clicking on them. So for example, you don't have to re-type "milk", remember your inkjet cartridge part #, or re-look-up your car's oil filter part #.
5) "Best Price" list. We keep a benchmark list of "Best Prices" at which stores so that we know, for example, when we go into our local grocery store, if their sale price on item X is as good as the normal price at Costco. (No need to cross-off items since it's not really a shopping list.) Such "Best price" items (are automatically sorted alphabetically) and might include an item like, "Margarine, Canola Harvest tub, 1lb, $2.79. ($2.79/lb)- Costco."
I recommend choosing the option to "long-press" items to cross them off the list, otherwise you can accidentally cross them off the list.