+1 for Bridge.

Bridge is a game of short-term and long-term memory, strategy (in long matches), tactics, deduction, induction, risk assessment, hidden information, and finally a strong test of character, and your judgment of the characters of others. Unlike chess it does not seem to have a "limit" where you stop getting smarter and start merely learning more about chess. There's a reason it's the favorite game of some of the world's smartest and richest men.