One of my absolute favorite uses for the tablet are mapping Apps. It's the one area in which the iPad has brought me all the joy I had hoped for, and then some.
Hands down, my favorite is Google Earth--but who doesn't love playing with Google Earth? I'm hoping to make use of it in some of my environmental courses, where I think it will be a useful way of situating the controversies we talk about in real space.
After that, I've enjoyed experimenting with several mapping programs that allow me to get additional information about places I was mapping, including satellite and terrain images, and topographical information. I've had good luck with Maps+, MyTopo Maps, and World Map.
I am really hoping to be able to use these mapping apps when I visit India to do some guest lectures, but I honestly don't know what kind of functionality to expect in India. Does anyone have any advice for traveling with the device in this part of the world?