Gamers of a certain age probably will have fond memories of Cosmic Encounter, which was first released in 1977. The game has gone through numerous incarnations, currently residing at Fantasy Flight. At the core of the game is the interplay between the various interstellar races. The owner of the Dice Monkey site has created some very nice Dr. Who themed alien races for Cosmic Encounter.
Overlords of Infamy is (for the time being) a free print-and-play game. The author writes:
In this game, you take on the role of an Evil Overlord ruling over subjects within his/her sizeable tract of land. The goal is to make your subjects as miserable as possible, while other Overlords are doing the same to their subjects. You accomplish this by harvesting a variety of materials to complete myriad Nefarious Plots ranging from “Steal Candy from Babies” and “Make Everyone’s Socks Slightly Damp” to “Blow up the Moon!” and “Resurrect the Old Gods”. All the while, there is a band of Adventuring Heroes from the Kingdom of Good going around trying to thwart all Overlord’s plans, other Overlords will be committing acts of Espionage against one another, and random world events will be triggered by World Tension from your actions!
Kill Doctor Lucky is a new classic board game that has been through several editions since first publication in 1997. You can get a print-and-play of the original version at the link.
Farscape is one of my favorite science fiction series, though like many, its life was too short. You can relive the adventures with the print-and-play Farscape card game.
Unexploded Cow is a commercial product from Cheapass Games, but you can get a free print and play version at the link. The game has an hysterical premise: that bovines suffering from mad cow disease are being used to solve the problem of unexploded bombs in Europe left over from the wars.