Early in the second season of The Big Bang Theory, Sheldon (Emmy nominee Jim Parsons) asks Penny (Kaley Cuoco), "When did we become friends?" For a smart guy, Sheldon misses a lot. But for the record, season 1 answered the question of whether or not an adorkable group of geniuses can become friends with the hot girl next door (yes!). Season 2 shows us what that friendship looks like, and it's awesome, especially when it includes a rousing game of "Rock, Paper, Scissors, Lizard, Spock." Sheldon's roommate Leonard (Johnny Galecki) wants to be more than friends with Penny, but the richest relationship of the show is that of Penny and Sheldon. He uses the "covenant of friendship" to get Penny to give him rides, he engages in an over-caffeinated business venture with her, and in the excellent Christmas episode, they exchange gifts and share a surprisingly touching moment. (Sheldon's midseason efforts to befriend a colleague can't compare.) Penny is forever changed by the guys, even telling a date about Schrodinger's cat and delving into online gaming. The extras, including a gag reel and interviews with the cast and crew, reveal the stars to be as appealing and connected to each other as their characters. --Stephanie Reid-Simons