First, an optical illusion dance routine:
I thought everyone knew about "How It Should Have Ended" already, but apparently Avalyn and her sister didn't. So for anyone else who hasn't, or just hadn't gotten around to the Iron Man 3 one yet, here it is. (The best part is the superhero cafe bit at the end =) (And just in case, it has spoilers for Iron Man 3, duh).
Don't watch this one if you're prone to nightmares about snakes :)
If you like xkcd's What Ifs, here's someone doing something similar about "What if Superman punched you in the face?"
Okay, couldn't resist throwing a little literature stuff in, here's a discussion about "What classing space opera novel do you want to see on TV?" In reality i'm sure most of the ones suggested would go horribly wrong if adapted, especially the harder SF ones, but it's interesting to see a big long list of what space opera books other people like.
And here's a list of some pretty awesome looking real-life flags:
I haven't seen Season 3 of Game of Thrones yet, but since i've read the books i still found these infographics amusing:
And the final video reward, a cute little animated short. It's by some art students and is about ten minutes long.