A couple of weeks ago one of our members, Nick Warner, posted that he had developed an app for the iPhone called Gram Weenie to calculate your pack weights - base, consumables, worn/carried, and FSO.
He's now got the first revision of the app available on iTunes and the improvements are significant. You can now maintain a master list of all of your gear, by category, and the create "Trips" and choose the gear you want to take. He's even got a check that appears (and disappears) that you can use when in Trip mode to confirm that you have it (no more packing the stove but not the alcohol). It allows you to carry your gear list in your pocket and to tweak your trip lists any time you want. I've purchased a bunch of programs that allow me to view Excel files on my iPhone - primarily because I wanted to be able to play with my gear lists. This beats them all!
I don't have any financial interest in this - I was one of the guys who signed up to get the evaluation version and I'm proud to have worked with Nick on some of the improvements he's included in this latest release. One of the things he's included at my request is the ability to enter estimated weights. I use that for when I have a piece of gear that I haven't yet thrown on the gram scale or if there's something that I plan on acquiring before my next trip.
Here's the iTunes link to the Gram Weenie app. I think you'll find it one of the more useful backpacking apps out there.