Best Drinking Games

Beer Pong - A test of drunken skill and aim. Perhaps the greatest drinking game ever invented?
How to Play Beer Pong:

Keg Cups (usually 6 or 10) are partially filled with beer and set up in a diamond shape on each ends of the beer pong table. When a ping pong ball lands in an opposing player's cup, that cup must be drank by the opposing player. The winner is the player with the most cups left.

Flip Cup - A great drinking game for groups who are energetic and like doing something active. This game can get loud, as with most drinking games, but the competitiveness this game brings is fun!
Flip Cup is one of the best team drinking games out there. What makes it better than beer pong is the fact that it involves a team of players, usually up to 5 or 6, rather than the one or two people in a beer pong team. With more players involved, it enhances the competitiveness of the sport. See, in beer pong, one player can carry a team to victory, while each member of a Flip Cup team must produce in timely fashion to ensure victory.

Game Summary:

It's a team-based drinking relay race. Two teams line up opposite of each other at a table. First person chugs their beer out of their keg cup. The next person can't go until the person before them has drank all their beer and set their cup on the edge of the table and successfully "flipped it" until it has landed upright.
Quarters - Test your ability and accuracy by bouncing quarters off a table and into your opponents drink. A great ice breaker...just go up to someone and say "drink" and slam a quarter on the table and sink it in their drink. OK, not really, but a fun game to play at home or at the bar.

King's Cup - Another great drinking game for big groups. This card game is not only fun and entertaining...it'll get you drunk!
Game Play:

Place a beer on the table and cards face down in a circle around it. Who ever draws the 4th King has to chug the beer in the middle. Each card turned over before the 4th King has a specific rule, giving many variations to the game.

Presidents & Assholes (card game) - There are many different house variations of this game. The idea is to be the first to get rid of all your cards to become President. The person who finishes last in the round is the Asshole.
Bullshit (card game) - Call out your friends if they are bluffing you. The point of this game is try to lie and try and get away with it. But, if your opponents call "Bullshit" and catch you lying, you have to drink.
3-man (Dice game) - A pretty simple dice game that will always get the "3-man" drunk. Time to bust out your dice rolling skills because every time you roll a "3" the 3-man drinks.
High or Low (card game) - Another one of those pointless drinking games where the idea is to get drunk. Grab a deck of cards and start turning over the cards one by one. You guess whether the next card will be higher or lower, and if you guess wrong you drink.
Shotgun - A race to see who can drink the fastest. Something that is argued over between guys at every party you go to.
F the Dealer (card game) - A card guessing game that involves a lot of drinking.