I see everyone has mentioned the EP from Sims 3 so I won't repeat those. But as a new idea I think it would be awesome to fly around in outer space in a space ship. But like with the GTW EP be able to control your Sims while they are on the ship. You would create the layout of the Ship, create the Sims to man it, and take off into the stars. The EP would randomly generate new worlds/planets for your Sims to explore. You Sims could be like a crew from Star Trek peacefully exploring the galaxy, or like the crew from Firefly taking jobs where they come to keep their ships flying and to feed themselves. The ships could have a crew of one or a crew of dozens. The super rich Sims could build their own ships and fly wherever they want, while the rest could sign up with the crew of a company's ship to make some money. The "jobs and careers" could be the captain of the ship, the engineer, all the way to the maintenance man.