This aired a few weeks ago, but TV Guide just put it on YouTube. No spoilers (this was filmed two months ago), and they basically threw every single behind-the-scenes clip they could find into this, going back to Season Two, but there are some great interviews with the cast, as well as Carter Bays, Craig Thomas, and Pam Fryman. Most notably, in the first video, Alyson Hannigan endorses The Hair.
And Josh Radnor kicks ass at HIMYM trivia, only to be stumped by the lyrics to Let’s Go to the Mall: