For group get-togethers, here are some great board games to have on hand.
Can't Stop -- 2 to 4 players. An elegantly simple "push your luck" game. You only need to make one decision: keep going, or stop?
Incan Gold -- 3 to 8 players. This is a reworked version of a classic called Diamonte. It's another "push your luck" game, but it's very different from Can't Stop in that it's group game. The whole group plays in parallel: they all decide whether to keep going, or stop, and all reveal their choice simultaneously. This means that the 8-player game doesn't really take longer than the 3-player game!
I'll second the vote for Pandemic. But if you want something a little simpler than Pandemic, with a less depressing theme, you can play Forbidden Island (2-4 players). Forbidden Island was designed by the same guy who designed Pandemic, and uses many of the same game mechanics. I love the art, which reminds me of Myst; and it is inexpensive and doesn't take up much space in your closet. Very suitable for kids.
All of these suggestions are good for convincing non-gamers to try playing a board game.
P.S. When I was a teenager, some friends and I used to play Wiz-War, and had a blast. It's a simple game: either steal two treasures from other players, or be the last player standing. There is a deck of cards, which includes all kinds of crazy spells you can cast.
Once when I was playing, another player hit me with Slow Death, which makes you lose one hit point for each card you draw; I countered with Reversal, which reverses the effects of a spell, and started drawing two cards each turn (the max). I thought this was a good thing, but the other players were now very worried about me, and they all ganged up on me and just killed me. So the Slow Death worked after all, in a fashion.
The game is now available in a deluxe edition (which I haven't played yet).