Games with features like Battlestar Galactica's "Traitor" Mechanic?
There are many games with a "traitor" or "uninformed majority" type mechanics. In some of them, such as Mafia and Are You The Traitor?, that is the main point of the game; you are trying to discover each person's role, with not much else on top of that. In others, it's a more incidental feature, usually involving the win conditions for each player or team, but with more traditional gameplay mechanics for the main duration of the game. In the following descriptions, I sketch only out how the "traitor" mechanics work for each game, not how the whole game works.

There's Mafia, also known as Werewolf or Assassin, which is probably the most well known, and one of the oldest, of the genre. In its most basic form (using Werewolf terminology), you have two Werewolves, one Seer, and the rest are Villagers, though only the Werewolves know who each other are. Each day, everyone (Villagers, Seer, and Werewolves) try to decide who the Werewolves are, and hang one person. Each night, the Werewolves silently and secretly choose one person to kill. Each night, the Seer gets to discover, silently and secret, whether one player is the Werewolf. The humans (Villagers and Seer) win if they kill both of the Werewolves, the Werewolves win if they equal the humans in number. The Seer is trying to help guide the Villagers to kill the Werewolves instead of innocent Villagers, without revealing himself as he will be killed by the Werewolves the next night (unless he identifies both of them openly; but of course, a Werewolf could also claim to be the Seer...).

In Are You The Traitor? from Looney Labs, there is a Key-Holder, trying to deliver a key to the Good Wizard, while the Evil Wizard tries to get the key instead (only the wizards know which is which). The Guards are trying to help the Key-Holder get the key to the Good Wizard, but there's a Traitor in their midst, who's trying to (secretly) reveal to the Evil Wizard who has the key, without being caught by the Guards. The Good team wins if the Key-Holder delivers the key to the Good Wizard, or the Guards catch the Traitor. The evil team wins if the Key-Holder accidentally delivers the key to the Evil Wizard, the Guards attack someone other than the Traitor, or the Evil Wizard catches the Key-Holder is before the Key-Holder delivers the key (the Traitor can never win directly, only by communicating secretly to the Evil Wizard). It's an interesting twist on traitor mechanics, lots of different roles, all with very different goals, but still has the basics of the traitor mechanics.

The multi-player version of Homeworlds, an Icehouse game has a traitor mechanic, though the 2 player version, Binary Homeworlds, is more popular. In the multi-player version, players are secretly assigned Good and Evil roles. The basic mechanics of the game are an abstract strategy game, in which players are trying to eliminate each other (I won't go into the details, as they aren't relevant to the traitor mechanic). The Good players are on a team; they win if all Evil players are eliminated. Each Evil player is playing for themselves; they win if they eliminate any other player, Good or Evil. So, Good players are all cooperating, and Evil players are all competing.

Bang! is a spaghetti western card game, with a Sheriff who is known to everyone, and Deputies, Outlaws, and a Renegade. The Outlaws are trying to kill the Sheriff, the Sheriff and Deputies are trying to kill the Outlaws and Renegade, and the Renegade is trying to be the last man standing.

Napoleon is a trick-taking card game (played with ordinary playing cards) originally from Japan (and apparently over 100 years old, though not in its exact present form). 10 cards are dealt to each player, and two blinds are left. The players bid a number of tricks and a trump suit, similar to Bridge. The winning bidder is Napoleon. He names another card, and the player who has that card becomes his General (but only the General knows that); they together need to make the bid to win the game. Napoleon now gets to take the two blinds, and discard two cards; if the card he named was one of the blinds, he's playing alone, with no General. The game is then played as a trick taking game with the named trump. No one but the General knows who that is, and Napoleon and the General (or Napoleon alone) are playing on a team against the other players, who are also on a team.

Shadows Over Camelot is a cooperative game, but there is a variant in which one player might be a traitor (or there may be no traitor). The players are working together against the game, but the traitor will try and sabotage the progress of the other players while remaining undiscovered. The loyal knights may accuse someone of being the traitor; if they're correct, they get an advantage, if they're wrong, they're set back; of course, depending on the game, there might not even be a traitor. If the traitor remains secret until the end of the game, he can set the players back and turn victory into defeat.

In The Resistance you are a group of resistance fighter running missions against a corrupt and evil government. However, there are government spies in your midst. You need to complete three out of five missions successfully, without a spy sabotaging the mission. Each round, a new player is the leader, and must select a team, trying to choose only loyal resistance fighters and no spies. After selecting the team, the players vote on whether that team should be formed. If the spies sow discord, and no team can be formed after 5 tries, the spies win and the government crushes the resistance. Otherwise, they go on the mission; but any spies on the mission have the chance to sabotage it, causing it to fail. If they do, however, they risk being found out.