You definitely need to get Settlers man. Once it starts getting old, get the Cities and Knights expansion. Thumbs down on the Seafarers of Catan expansion though.

You don't need to be a rocket scientist to figure out how to play and everyone who has ever played it loves.

I don't know if anyone's mentioned it yet but you need a minimum of 3 players to play.

Some other good Euro games are Carcassonne(2-5 players) and Puerto Rico which is fairly hardcore as far as games go.

This is one of the best sites to review and purchase games:
www.thoughthammer.com