I use Google for calendar and contacts and sync it with my iPod. The last software update installed a new free app on my iPod called "Reminders" that is basically a to-do list. I haven't used it yet except to play around with it, but it looks like it's pretty decent. I also use the "Notes" app that came installed already on the iPod.
I tried an app called "ShopListFree" for a shopping list. A friend has the paid version and likes it. I haven't liked the free version so much, but maybe it's one of those where they took so much functionality out of the free version that you don't get a good enough taste of the real thing to actually see the utility in it.