Adult board games (Mayfair, Hans im Gluck, Rio Grande, etc.)

[Only Mostly Dead]

I'm spending a little time in another state, and today, while looking around a local mall, I found a wonderfully well-stocked board game store, stocked full with all kinds of games that are otherwise quite difficult to find.

However, because these games run at least $20 per, and some go up to $80 or $90, I'm in over my head on which true gems I may want to buy before I leave.

I already own, and love, Settlers of Catan (plus expansions). Carcassone gets played, but not nearly as much. We also play a decent bit of Ravensburger's The Amazeing Labyrinth as a quick game.

What would my fellow geeks recommend? I didn't ask if they can order games they don't stock, but the stock looked very good on the popular ones I don't have (Tigris and Euphrates, Ra, Puerto Rico, etc.) and far far more. But I don't know where to start at $40 per box. Babel looked interesting, and billed itself as a two-person game. Anybody played that one?

Please explain why a given game is good. And bonus points if there is a strong game mechanic for two people. Obviously, larger group games are still good, since we manage regular Settlers tables.