When I'm stuck, I do one of four things ...
1

Shut down everything and take the dog for a walk. This lets me articulate outloud, bumble through passages, beat stuff around in my head, and generally think. A new environment sometimes gets the juices flowing, new scenery. Plus I get some exercise and the dog is extra happy.
2

Write some generally craptastic filler in underlined italics that can be cut out later. ie; "she screamed as his corpse tumbled over the edge ...
of the local Burger Joint where they had been taking a coffee break not moments before blah blah something something then she decided to get a cheeseburger since watching corpses fall over edges is hungry work and besides she now had his wallet and it wasn't like he was going to be using it yadda yadda filler can't think @_@ I could go for a cheeseburger right now ... (By now I usually come up with the next sentence and happily continue the story!
3

Pray to the writing gods to bestow their bountiful words of wisdom upon my lowly self. Sacrifice old manuscripts in hopes of gaining their favor.
4

Skip to a new scene, whatever's in your head urging you to write. A couple lines of ###'s or

will remind you to come back and finish that scene later. There isn't a rule that says you have to write from beginning to end, so skip around a little! If you're feeling the urge to write, for the sake of cake, write! Doesn't matter what -- that's what revisions are for.
Hope that helps! Good luck with the dumping of the body over the cliff thing. I hope it wasn't anyone "she" liked. ...