1 Cliche Down, 999,999 to Go

After viewing the latest episode of Lost, screenwriter John August (Big Fish, Charlie and the Chocolate Factory) has just condemned the use of air ducts as an escape route for protagonists in all forms of entertainment, be it movies, television, or...well, I guess just those two. I'd join in, but I haven't had time to write any screenplays, much less include air ducts in them. This does remind me, however, of a similar cliché as described by Dona Knight in Roger Ebert's Bigger Little Movie Glossary:

• Air Vent Escape Route. If the hero is imprisoned in a building owned by the villains, there will inevitably be an air vent cover that is not screwed in and is easily removed. The passageway will be large enough toaccommodatee any size person. The escape route will pass over the room where the bad guys are discussing the details of their diabolical plan, which the hero will now be able to foil.

What's your favorite movie that makes prominent use of the air duct escape route? Or just your favorite movie that has air ducts in them? I can't help but think of that great scene in Alien where Dallas is searching for the alien in all the air ducts of the ship, turns around, and BOOGA-BOOGA!!