make a list of community issues and think about how you can create a piece of software that can help combat those issues. It doesn't have to be direct intervention. Think about things like the administration and office work that goes on behind the scenes.
My advisor helps me and he always suggest find issues to the developers community and i cannot find any since im not familiar with all the tools used and im not that pro when it comes to developing apps :(
I got one, but I don't knwo if it is still up-to-date :D Make an application:
WindowsMobile <-> ActiveSync <-> Contact manager or calendar manager
WindowsMobile <-> Bluetooth <-> Contact manager or calendar manager