I have several on my iTouch.
Block Fab has a library of blocks. You put in the size of your block and it tells how much fabric you need of each color for one block. You can also play with layouts and colors to some extent. Kind of fun for when you need to kill time in a waiting room or something.
Fabric Journal - This one seems to be misnamed to me. It's actually an app for pictures (up to 4) and notes of your projects including size, start and finish dates. And there's a graph to show % completed.
Fabric Stash - This would be a fabulous app if only I'd take the time to use it. You can keep photos and information including manufacturer, line, size, location, cost and project name. It's also searchable by name, color, etc. I haven't actually used this since I need to take pics of all my fabric and import them into the iTouch, then input all the measurements, etc. A big project that I keep putting off. It would probably work better with an iPhone so you could take pics directly. But it would be handy to have all your stash with you when you're shopping.
I just downloaded iQuilt but haven't yet figured out how to use it. Seems like it's similar to those fabric calculators. I know this will be handy once I figure it out