My bundles are located in two places. For Ruby and other bundles that come preinstalled with TextMate:
~/Library/Application Support/TextMate/Managed/Bundles
Saved 3rd party bundles are in:
~/Library/Application Support/Avian/Bundles
Check those folders and see if you have a Ruby.tmbundle
file.
Make sure the ruby source code file is saved with the .rb
file extension as well, so TextMate knows to use the Ruby bundle when syntax highlighting, soft-tabbing, etc.