iPhone: There's no shortage of shopping planning apps for mobiles designed to use barcodes to speed up the process, but most of them are resolutely US-centric. Scan2List is an Australian-designed app that lets you build a shopping list by scanning the barcodes of items in your kitchen cupboards.
As well as building a list through scanning (or entering manually), the list can be sorted into aisle categories to make your supermarket experience faster. You can also check off items as you buy them, and save lists for reuse in the future.
Scan2List is a free download for iPhone. If you give it a whirl, tell us how well it performs in the comments (my only iOS device right now is an iPod Touch which obviously isn't much help here!)