Conan O’Brien appeared on Young Justice! (sort of)
Okay so didn't really "appear." They just photoshopped Superman to look like The Flaming "C" (O'Brien's alter-ego that Conan and Tim Kring came up with)
Smallville Final Season Promo Image Hints At The Arrival Of Superman
This is it, Smallville fans. It’s just about time to see Clark Kent squeeze into his trademark red and blue tights so he can run faster than a speeding bullet…