gem install pry
pry -r ./config/environment
Don't miss the various extensions which are out there:
You can give it basic debugger stepping abilities, you can do remote sessions, you can have it automatically drop in a REPL before an exception, repair it, and carry on, it's amazing. Really shows off the power of ruby.
Similar site I have been waiting for since Feb: http://rubyreloaded.com/trickshots/