For Rails Rumble last year I created a Rails app for generating test data in various formats. It definitely isn't as polished as this (only had 48 hours), but allows for the user to specify their own format. After the competition I cleaned it up a bit more and converted the data generation functionality into a standalone Ruby gem. I'd appreciate any feedback...
App: http://proglipsum.com/
Gem: https://github.com/theandym/mannequin