Coup (3-6 players, ages 10+, published by Indie Boards & Cards) is a delightfully vicious little card game that blends the bluff and uncertainty of Hold 'Em with the aggressive calling-out of Bullshit and a touch of deeper strategy. It's a game that clicks with gamers and non-gamers alike, and a friend of mine summed up the experience well as "a game you should be able to play for money."
Players take on the role of power brokers in a futuristic dystopia. Each starts with two face-down cards from a 15-card deck (3 each of five different cards), and a bit of money. The cards represent members of the government under your control, and you amass money in order to assassinate or stage coups against the other players' cards; turning them face-up and rendering them useless. Players with both cards revealed are out of the game; and the winner is the last person standing.
Each of the five cards enables players to take a different special action, and/or block another player's action, and there are also a couple of actions that anybody can take no matter what cards they have. The heart of the game is that since your cards are face-down, you can claim to have any card you want, and take any action you want. If someone challenges you, you either reveal the card and your opponent loses a card, or you concede that you were bluffing and lose a card yourself.
The trick, then, is to read both the game state and the players at the table to determine what to do. You can play it safe, tell the truth most of the time, and use diplomacy to target the people who are ahead of you; lie unpredictably and draw your opponents into challenging your truthful plays; or read your opponents and knock them out when they lie. And over a few rounds, you can ride the shifting sands of the metagame between all three of these strategies.
For example, the Duke is allowed to take 3 coins as income rather than the 1 or 2 everyone is allowed to take, and can block anyone else from taking 2 income. It's common with a group of new players for everyone at the table to claim Duke on the first turn, giving them enough money for an assassination on their second turn or an unstoppable coup on their third. Clearly, someone or everyone is lying, but who? After a few games, claiming Duke on the first turn becomes a great way to get called out, since it's such an obvious and self-serving deceit. But with 3 Dukes in a 15-card deck, it's still likely someone really has it.
As more and more cards get turned face-up heading into the endgame, more and more information becomes available to judge who is lying, and the winner at the end is the person who not only has done a good job bluffing and reading their opponents, but has also set themselves up strategically to deliver the final blow before their last opponent does. This goes pretty deep, as a skim through this article about endgame strategy will readily show.
Normally I'm not a fan of games with player elimination, but a full round of Coup only runs about 10 minutes, and the resolution is fun to watch and kibitz about even after you've been knocked out.