Some of you may have played this game before. People play for free at theresistance online.com
From the Rules Page
The game requires between five and ten players.
Approximately one third of the players are randomly chosen as spies; the rest are members of the Resistance.
The spies know who the other spies are, but Resistance members do not.
The game consists of up to five missions.
Each mission has a leader. The leader proposes a mission team of a certain size, which the group approves by public vote.
If the group does not approve the mission by a simple majority, leadership passes to the next player.
If the group cannot approve a mission team after five attempts, the spies win.
Once a mission team is chosen, it votes by secret ballot whether the mission succeeds or fails.
Resistance members will always vote for success, but spies have the option of voting for success or failure.
It usually only takes one spy on the mission team to sabotage a mission, but sometimes the fourth mission requires two.
If three missions succeed, the Resistance wins. If three fail, the spies win.
As you can imagine, there is plenty of opportunity to practice your trolling skills and powers of deduction. If the rules don't make it clear whether you'd like this or not, there's a video of live gameplay on the main page. Many people find it quite addictive.