HillaryIsMomJeans is absolutely awesome. I could keep clicking for hours. Now to come up with some more new entries...
BarackObamaIsYourNewBicycle is the flip side, but is far, far less fun.
GreenMoney is a great site for anyone who is into organic farming and stopping hunger around the world. If you check out that GreenMoney link, you will understand why rickrolling is such fun. On April 1, all featured videos on YouTube's main page linked to the same Rick Astley video. Great stuff.
Video Nugget: Frozen in Grand Central Station