TextMate is my editor of choice. It is lightweigth and does just what I need. Not a fancy IDE that consumes half my resources and takes for ever to update. Here is a handy tip for adding bundles to it.
Navigate to the path where the bundles are stored, which in the case of a Mac is :
cd /Users/myName/Library/Application\ Support/TextMate/Bundles
Clone the bundle from the repository of choice (e.g. github):
git clone git://github.com/drnic/ruby-on-rails-tmbundle.git "Ruby on Rails.tmbundle"
And tell TextMate to reload:
osascript -e 'tell app "TextMate" to reload bundles'