Liar's Poker comes in a couple of different flavors. The first may be more comfortable as it is a tradition card game and the later is not. The game begins with each player starting with two quarters. Everyone is then dealt two cards down. The first player calls a poker hand. The next player has the option of either calling a hand which beats the previous hand or challenging the previous player's call. If a person challenges the hand, then everyone's cards are pooled to determine if the hand exists. If it does, the person who called the game loses one of his quarters and starts the next game, with only one card dealt to him. If it does not, the player who called the hand loses the quarter. After a player has their second quarter taken away, the player is out. Deck is reshuffled after each round. Game ends and the pooled change is awarded when only one person has a quarter left.
Liar's poker is also a popular bar game that only requires a dollar bill to play. In the place of cards, the eight-digit serial number on the dollar bill (see below is blue) represents each "hand." The object is similar to the card version--to make the highest bid of a number that does not exceed the combined total held by all the players. The numbers are usually ranked in the following order: 2, 3, 4, 5, 6, 7, 8, 9, 0 (10) and 1 (Ace). For example, if the first player bids three 4's, he is predicting there are at least three 4's among all the players, including himself. The next player can bid a higher number at that level (three 5's), any number at a higher level (four 2's) or challenge. The end of the game is reached when a player makes a bid that is challenged all around. If the bid is successful, he wins a dollar from each of the other players, but if the bid is unsuccessful, he loses a dollar to each of the other players.
Both games are fun diversions that combine statistical reasoning with bluffing. The barrier of entry is small in that the most you can lose is a matter of dollars and cents. However, for you high rollers, currency substitutions are always an option.
If you practice any other variations on Liars Poker let me know in the comments. This is one game that can easily vary in rules.