Automated Testing
Today I've had my first tase of automated testing, on a little django-related project of mine. And I love it! I've been putting it off for a very long time now, so there's some satisfaction to the fact that I've finally started. There's also my choice of language, Python: the test code is minimal, very little syntactic overhead. It's also fun, because I'm adding a bit of new production code into the mix, so it's becoming test-driven development. It's already finding bugs for me in my existing code, which is also good.
I won't say much about what test-driven development is; I'm a late-comer to the party and there's plenty of good information about it on the web. If you write code and don't use this technique, I strongly recommend checking it out.