Haml-bootstrap-rails provides Haml generators for Rails 3 with twitter bootstrap support. It also enables Haml as the templating engine for you, so you don't have to screw around in your own application.rb when your Gemfile already clearly indicated what templating engine you have installed. Hurrah.
Gemfile gem 'haml-bootstrap-rails', '~> 0.3.11'
install gem install haml-bootstrap-rails