Working on Rails code for a bit has started me on the spiral into obsessively customising my dev environment (I say obsessive as at the last Rails meetup I went to there was
One of the most popular ones is ruby-on-rails-tmbundle. Available here: http://github.com/drnic/ruby-on-rails-tmbundle/tree/
This bundle adds a ton of useful commands and features. Also recommended is the peepcode tutorial on using this bundle (not free but well worth the cost): http://peepcode.com/products/textmate-for-rails-2