Right now I'd say the three games that everyone should try are:

Shock
Polaris
Fiasco

Those are solid winners, each with fairly different styles of play. Between them you're getting a good feel for what's possible in a non-traditional game (meaning no GM, no prepared game).

So everybody put that on your to do list: if you haven't played one of them, speak up at the next meetup and demand to play!

Likewise, play each one more than once. The first time you play any game, there's a lot of teaching going on. When you come back and play the same system again, you can focus on having fun and being creative because you're already familiar with the rules.

(copied from another thread, because it's a good reminder)