David wrote a blog post on our participation in the GSoC 2009. It refers to the GSoC 2009 Wiki entry where the mentors have posted a few ideas (yes, we actively encourage students to come up with their own!). As I am the program manager, I am not active as a mentor, but I sure do have an opinion... here are my top five projects when it comes to "visibility" (a feature that will be used by a large percentage of our user base):

1. The database scout / database api / EDM designer (we already have a student lined up for this)
2. Debugger improvements (visualizers, edit and continue support, ...)
3. VB.NET 9 support on par with our existing C# 3.0 support (most likely a task for a CS student)
4. Refactoring support (think ReSharper)
5. Customizable keyboard shortcuts / toolbars

I took "Everything .NET 4.0" from my top five because Beta 1 of Framework 4.0 most likely won't hit the streets before the student application deadline. And I will post further ideas in David's blog post, so you might find something palatable there too.