If you use the bash command line a lot, and especially if you'd like to add custom tab completion for different commands, please check out my new project Compleat. It's a way to create new bash completion rules without writing tedious shell functions.
I'm going to write up some more documentation and post this to Hacker News and other places in a few days, so I'd appreciate it if you can test-drive the installation process for me. Follow the link above to get the source code from GitHub; the README file has installation instructions. Please let me know if you run into any problems or bugs!