How do you jumpstart a scene?

In regard to plot stagnation, Raymond Chandler famously said, "When in doubt, have a man come through a door with a gun in his hand."

TV Tropes has a lot of fun discussing what they've dubbed "Chandler's Law," and comparing it to parallel plot devices in TV, comics, films and video games.  I've heard that NaNoWriMo participants often run out of steam during the second week, and have to rely on quick, sometimes outrageous plot devises to keep their "writer's high" (and word count) going. The on...