Maps and mapping technology are ones that do sharply stick out as more than a natural fit for the tablet form factor combined with touch screen compared with today's mobile devices. This space has plenty to gain in innovation with the iPad.
Watching video from online (iPlayer etc.) would be my ideal application for this - an iPhone is too small, a laptop is too clunky and uncomfortable and I hate watching video sitting at a desk.
Another thing that might be a hit is multiplayer games. I was playing an air hockey game with my son on his iPod Touch and it was surprisingly good. With a bigger screen that could really be an interesting thing to watch.
Lots of board games might work pretty well on something like the iPad as people could sit round it.
Put a camera on the next generation. Augmented Reality is where it's at. Imagine an App like a Frommer's guide that did information overlays on whatever you were pointing at! Then you could zoom out to a map view and see what was around you, then zoom back in to a "Street View" to where you want to go.
