First is a cool mashup of Gangnam Style and the Ghostbusters song.

PSY vs Ghostbusters - Gangnam Busters - Mashup by FAROFF

Second is something that actually has nothing to do with Gangnam Style :) Someone did a Battlestar Galactica themed parody of "Sound of Silence" called "Sound of Cylons". Presumably there are spoilers here, but i haven't seen the last season of BSG myself yet, and didn't see anything too obvious, though i did try to turn the analytical part of my brain off before watching.

Sound of Cylons

Finally two Gangnam Style parodies that aren't particularly outstanding in the parody department, but _do_ have fairly impressive graphics for fan videos. The first one is for Minecraft, the second one is for G1 Transformers.

PSY - GANGNAM STYLE (강남스타일) ft. TRANSFORMERS

"Minecraft Style" - A Parody of PSY's Gangnam Style (Music Video)