This phenomenon must be getting popular, because this horror spoof about a vaguely black metal spoon murderer has apparently won some prizes, assuming the info on the web site is correct:
http://www.richard-gale.com/
(click the link at the top to watch it on youtube)

also there's this classic, which most people on here have probably seen, the Pac Man movie trailer:
http://www.youtube.com/watch?v=fWL6j0SvqV0
which has incidentally spawned a bunch of poorly done copies.

Are there any other ones worth watching?

This is my favorite. A gritty reboot of Mortal Kombat in a non-fantasy setting? How could that work? Well you make Reptile a serial killer with a rare birth defect and Baraka a plastic surgeon who lost his mind and implanted ten inch blades in his forearms. This is pretty much the best way to fuck up an existing storyline but actually make it awesome, it's like the Twisted Metal: Black of Mortal Kombat, which is saying a lot.

This one's a classic, for sure:

http://www.youtube.com/watch?v=HBCzkz3gHb8

watch:

http://www.youtube.com/watch?v=rbhrz1-4hN4

http://www.youtube.com/watch?v=TnpTcrtsN3U

I seem to have an odd sense of humor and thus most of the stuff on the internet I don't find particularly funny, but those are a couple exceptions.

Can someone please tell me if this Smiley thing on YouTube is a trailer for a real upcoming movie? If so, a slasher flick starring YouTube sensations sounds like the new lamest thing to happen to movies.

EDIT: also, the trailer with the killer that hunts the guy with a spoon is pretty funny+RoosterTeeth made a decent trailer for Angry Birds.

http://www.youtube.com/watch?v=sDX1m0Y2Vkg

Anyone that likes Pokemon should have seen this already.