I'm surprised that Puerto Rico hasn't been mentioned. My hacker friends and I dabbled in both Settlers and Carcassonne, but ultimately ended up playing mostly Puerto Rico. Great game. Unfortunately, I haven't had much luck getting my non-hacker friends to play.

A big hit in almost any group of people has been Speed Scrabble. Quick, easy to play in teams, and just great fun overall. If you like Scrabble, try it out.