[Ed the Coastie]

My regular players know that I am perfectly capable of springing an unexpected situation on them.

In one case, the players created characters for what had been hinted could be considered an espionage/counter-terrorism campaign. The first adventure seemed to be exactly that, with the PCs escorting a captured militiaman/terrorist on his way to testify and trying to protect him during a running gun battle through O'Hare airport with his former companions. The PCs were successful in making it through the gauntlet and bundled their prisoner onto a chartered 747...only to have it shot down on takeoff by a terrorist with a Stinger missile.

The next session -- the actual start of the campaign -- saw the PCs waking up naked and hairless on Riverworld. (My wife still hasn't forgiven me for that one...)

One of my favorite standard games (usually a campaign starter) is "Strangers in a Strange Land", where the PCs find themselves castaways on a tropical beach with minimal equipment. (Yeah, I know it sounds a lot like Lost...but I was running this scenario for more than a decade before the show came out.) The PCs have been escapees from a slave ship (D&D), shipwrecked cruiseship tourists (Danger International), crash-landed space tourists (GURPS) or crew (AD&D Spelljammer), and even once soldiers (from a Twilight 2000 campaign) who emerged from cryogenic suspension into the world of Cadillacs & Dinosaurs.