Ask HN: Tips on good source code?

I got some free time before my next semester, and I got a couple of ideas I want to try out. But most of them includes multiple users and databases. That aint my strongest side, so I'm looking for some good source code I can read and learn from. Can you guys recommend something? Source code or just a good read!

My skills: Python > Java > C > * I recently downloaded, installed and used my first database with MongoDB (beside MS Access about 5 years ago). So I guess that a project that uses mongodb and django would be awsome.

-Kristian