Here's a great freebe iPhone app for you via eNature; field guides to USA's national parks. The whole idea of having a digital field guide does have some appeal, although carrying field guides in your pack does demonstrate a certain gravitas as a devoted naturalist. And as mentioned previously, the ability to ID plants via pictures is coming of age, but here's the catch. What will work in Central Park won't work in Yellowstone. What you get to download is merely the access package, the goods, so to speak, are on a server somewhere so it requires internet access. Looks like my old field guides are not quite as out-dated as they sound unless you're carrying a satellite iPhone. Do they make those?