If you are looking for ‘party’ games, as opposed to gamer’s games, I would recommend the following:
Apples to Apples (as previously noted) - my family keeps clamoring for me to dig this one out when they come over, or at least they did until I bought…
Royal Turf - more of a board gamer’s game, but light and easy enough to learn for anyone to pick up. You place hidden bets on 3 of 7 horses (and one false bet of 0 to mislead your opponents). You roll a special die and then move forward one of the horses. Play rotates among the players, who must choose to move a horse not yet moved (until they all have). This continues until three horses have finished. Money is paid to people who have bets on those horses, and the fewer that bet on the horses earn more money than the ‘favorites’. You can find it at www.funagain.com (as well as many MANY board games).
Werewolf - best in larger groups, and it is FREE! You can find rules here: http://www.eblong.com/zarf/werewolf.html. A quick example would be (say a 7 player game) that there are two werewolves, one seer, and four villagers, and one non-playing gamemaster all randomly and secretly chosen (scraps of paper or deck of cards works well). When the game begins, all the players, except the GM, close their eyes. The GM then tells the werewolves ONLY to open their eyes. Then, using hand gestures or eye-movement, the werewolves choose one other person to ‘kill’. After, the werewolves close their eyes and the seer is told to open his eyes. Again, quietly, the seer points out any one player in the game. The GM will let the seer know whether that person is a werewolf or villager. Finally, all the players open their eyes. The GM announces who was killed by the wolves (that player is out of the game). Then, EVERYONE not dead discusses who they think the werewolves might be and vote on one person to ‘hang’. That person is then out of the game. The seer, who of course is slowly learning certain information, must be careful on how to relay that info for surely if the wolves know who the seer is, the seer will be the next victim.
If the wolves can kill all the villagers and seer, they win. If the villagers can kill the wolves, they win.