Got one of those B&N 40% off coupons burning a hole in your pocket?
I picked up Carcassonne, Ticket to Ride, and Dominion this week. The first two are casual board games that focus on strategic plotting of land or routes. Very easy to pick up, and lots of replay. Dominion is a deck builder card game that is a lot of fun. I usually play that once a week with friends. Finally broke down and bought my own set.
These games are a lot more causal than something like monopoly. A round can be played in as little as 30 minutes. I think Settlers is a little longer, although I haven't played that one personally. But they do offer some very fun strategy that isn't entirely stale from round to round.