If you're generally only really wanting to search .rb files, here's a script which I call 'findrb'

Drop this in a file in your $PATH, chmod +x it, and off you go.

E.g.

 
 glenn-roberts-4 ~/ba[master*]$ findrb 'show' 
 ./app/controllers/home_controller.rb:13: def show 
 ./app/controllers/live_profiles_controller.rb:2: before_filter :authenticate_user!, :except => [ :index, :show ] 
 ./app/controllers/live_profiles_controller.rb:22: def show 
 ./app/controllers/live_profiles_controller.rb:26: format.html # show.html.haml