We currently develop a GPS/tracking/mapping app for the iPhone, and a bunch of our users have emailed us to ask us what our plans for the iPad are. The obvious application would be a trip planning app - something where you could trace out trails and waypoints on the iPad, and then load that data into your iPhone or other GPS unit out in the field. You could even take the iPad with you I guess, considering how light and slim it is.
We're still iffy on doing something like this, but a big part of me wants to, particularly since I'd use the app for my own trips, and it would be a good excuse to buy an iPad :)
I guess we'll see. We also see opportunities in boating and aviation, and we're talking to a boating maps company about a deal that might lead to an iPad app as well.