Last weekend, I went geocaching with my iPod Touch and an app called Geosphere. I went looking for 2 caches, just to get the hang of the software. I found one cache that was in an urban location, but the other, at the end of a quarter-mile walk along an icy path, was under too much snow to bother with. Geosphere is far superior to what I was using on my old Palm PDA, and the iPod itself is smaller and lighter, with a larger and more readable screen.
Other apps I'm using: SplashID (password manager) and SplashMoney (finance manager), both of which I'd been using for years on the Palm, and Toodledo, a web-based to-do list with an associated iPhone/iPod Touch app. Why the iPod doesn't come with a to-do list, I don't know, but I'm quite impressed with Toodledo.