Personally, my favourites are games you play with a big group of people - my all-time favourite "board" game is werewolf. Say you have ten people. Two or three of them would be werewolves, while the others are innocent villagers. Each turn the werewolves cull another villager, and the villager have to vote to execute somebody. Of course, since the wolves pretend they're villagers themselves they try to throw a spanner into the works. There's some special villagers that can gain information on who is a wolf and who isn't, but the meat of the game is in the execution discussion, which are always hilarious. Since I'm usually the game master it's also the best way I know of learning people's names ;)
This is the best game experience I've ever had! Discovered it on a youth exchange in Germany some years ago and it's just so much fun. I really enjoy that it's very inclusive and that so many people can join. The discussions and accusing your friends is the funniest part. :D Definitely good for those late summer nights. Can't wait to play it again :)