I'd have to say that my favorite episode thus far is the "Slapsgiving 2" episode, in which Marshall creates a website that counts down to the next time he will slap Barney and then sends him the link. In this episode, Barney spends his entire Thanksgiving paranoid that he will be slapped when he least expects it. Nonetheless, he is slapped exactly as he suspects, after Marshall delivers a lovely Thanksgiving speech.
Something else I love about this show is that CBS actually created a blog for Barney's character on their website. Barney's Blog corresponds with his antics throughout the individual episodes, and it adds depth to the show's credibility. This is an example of a legen.... wait for it.... dary form of multi-modal creative writing. This can easily be emulated in the classroom by asking students to choose a character from a story and design a daily blog based upon their characteristics from a story.