“Space Seed” is an episode from the first season featuring Ricardo Montalbán as Khan Noonien Singh, a genetically engineered superhuman whom the crew of the Enterprise finds in cryo-sleep. Khan and his crew attempt to take over the ship before being defeated and this sequence of events sets up what is arguably the best Star Trek movie, Star Trek II: The Wrath of Khan.
“A Piece of the Action” is a second season episode that finds Kirk, Spock, and McCoy beaming down to a planet that looks like 1920s Prohibition-era America.
Finally there’s another second season episode, “Journey to Babel,” where we meet Spock’s parents, Amanda and Sarek (Jane Wyatt and Mark Lenard). We learn how Sarek truly feels about his son and see Spock’s human mother.
Sadly there are no extras on the DVD and if you’re a fan of the show you have the box sets of the seasons. These are the remastered versions of the episodes which means they look better than they ever have. Nonetheless, if you don’t have these, my recommendation is to either buy the box sets or just rent the DVDs as these “best of” sets are just designed to cash in on the movie’s recent success and fans deserve better than this.