Just got back from a week long NASA sponsored workshop on the effects of dust (primarily African dust) on global climate change. Anyway we were issued iPads for the workshop to produce vodcasts for NASA Edge. We spent a part of each day sharing apps that were useful or just cool. I thought these were awesome:

Starwalk - great astronomy app for viewing all cool things in space.
Papers by Fifty Three - really cool notbook thing that you can write notes in with a series of pens and brushes. You can add water color like washes to make things look cool

Wish I had my iPad here to remember some of the other ones.