If you've read my blog at all you know one of the things I love the most about working with Education customers is the breadth of solutions.  Some of the best software that supports the first pillar is actually written by our customers within Universities.  Here are three must haves:

Paint .NET
Developed at Washington State University.  I was lucky enough to visit the school earlier this spring and came away with a new perception on mobility.  This is a very powerful graphics program that I use almost exclusively over other programs.
http://www.eecs.wsu.edu/paint.net/

3D Journal
Developed at Cornell.  I actually just learned about this, it was the motivation for this entry.  This is one of the coolest applications I have seen of the TabletPC.  Not only does it detect and render objects, it can apply theoretical force.
http://ccsl.mae.cornell.edu/research/sketch/

Chempad
Developed at Brown University.  This is my favorite Tablet PC demo because I secretly love the study of chemistry.  This application allows you to draw a molecule and then render it in 3D.
http://graphics.cs.brown.edu/research/chempad/home.html

I doubt this is anywhere near the end of the list.  If you know of others, I welcome comments.