I can seriously recommend Agricola. It features a very novel gameplay concept, and to make it even better, they have different sets of cards to adjust the games difficulty level. I've played Agricola about 10 times or so now, but I'm eager to play it more often. And there's not a lot of games that can do that.
I'm pretty open and I guess I can't be disappointed by the top picks.
Yeah, I was lurking at Agricola and Puerto Rico but they seem similar to the Settlers of Catan (I may be mistaken).
If people like card games, I can also recommend the original Canasta. http://en.wikipedia.org/wiki/Canasta