Adventurous The Cat Returns, created by Double Fine artist Lee Perry, is the easiest cartridge to find, developer The Fullbright Company notes in a blog post. Perry's directive was to create "an overly 'cool' Bubsy-esque character" and we'd say he nailed it.
Journey of Crystal, seen above, was clearly created by Supergiant Games art director Jenn Lee. This hypothetical JRPG sequel to Secret of Time Crystal is chock full of the fantastical, with a towering castle beckoning off in the distance. Check out the Fullbright post for the rest.
Gone Home, currently available for PC, Mac and Linux on Steam, has you returning home after a year abroad, only to find no one there to greet you and a cryptic note on the door. You explore and examine the house interior to piece together the story of the people who live there.