I totally spaced putting Beyonce's "Single Ladies (Put a Ring on It)" as the "most important pop culture dance development" on my 2009 list. Better late than never, especially as "Single Ladies" continues to be a force.

It's amazing to me how often the video comes up in conversations with dancers and choreographers. And how many of them know all the moves. Kanye West may be an ass, but he was right.  It's impossible to list all the YouTube "Single Ladies." But here are a few of my favorites. Enjoy!

• "Single Ladies"... Explained.

• Performance Art-Style

• Drag.

• Split Screen.

• And, of course, the original.