Cosmic Patrol is probably one of the best rules-lite storytelling game we've come across. It's simple enough that anyone can narrate a session (even a complete beginner) yet has enough of a system behind it to appeal to established RPG players. Although the default setting is 1930's pulp space opera adventure, the rules are universal and can be used for almost any genre or setting with only a little imagination. This game is an absolute blast to play, and is a great way to introduce people to the RPG hobby.
You can listen to our full review of Cosmic Patrol here: http://www.idleredhands.com/?p=1095