This video has been out for a while, but it recently started to go viral. YouTuber "loomyaire" (cool name) has posted "The Complete 14 Batman Window Cameos", featuring a bunch of celebrities who "pop in" while Batman and Robin are climbing the wall of a building (hint/spoiler: they rotated the camera for this effect).
My favorite? Colonel Klink (aka Werner Klemperer), who sort of stays in character, because Robin asks the colonel to "say hi to Col. Hogan for me"). That blows my mind, whenever two characters from different TV shows exist within the same universe. There are a bunch of other universe-benders, but I'll let you watch the video to figure them out.
Keith Shaw rounds up the best in geek video in his ITworld.tv blog. Follow Keith on Twitter at @shawkeith. For the latest IT news, analysis and how-tos, follow ITworld on Twitter, Facebook, and Google+.