I don't know if you would consider this a parody, it's more of a skit, but I love this song, I think it's hilarious:
[YOUTUBE]4eLABXmjySE[/YOUTUBE]
I wanted to post the Key of Awesome Ke$ha video, but JW beat me to it. So here's another Key of Awesome video, but really everything they do is hilarious:
[YOUTUBE]W_cGo0q7krk&feature=relmfu[/YOUTUBE]