This is a difficult one but I have to got with @m76 - Deus Ex is truly a masterpiece. The plot is always well-written, the gameplay is always entertaining and in general, the game never feels repetitive.
I think keeping the things which are antique and have some sort of history definitely means there is going to be some money that can be earned in market. ebay people do it all the time.
HP used to have a computer game that came with their PCs where you could cut auto racing practice laps. I forget if there was a race mode though, but just practice laps only really have the objective of trying to learn your car's handling and learn the track.
The game I've been playing for the longest time, Transport Tycoon Deluxe, has no real end goal or objective, you just build and grow your transport infrastructure indefinitely. And when you get bored with it you start a new game.