3 days left!
I recurrently got asked not only how to contribute to Debian, but more importantly how to get involved, i.e. become part of the project and stay around for a while.
In case you're a student excited about Free Software and Debian, there are only 3 days left (deadline April 8th) for applying to the Google Summer of Code program and work with Debian this summer. According to my past experience as GSoC mentor and admin, the program offers a wonderful opportunity to become part of a Free Software project like Debian. Think twice before missing it!
The proposed idea list contains several projects that might have a significant impact on Debian. The list includes a pet peeve of mine (developer package repositories) and many many more.
If you are a student, I suggest you to read a recent blog post by Ana that contains a nice overview of some project ideas, as well as info for applying.