Transport Tycoon Deluxe is a nice blend of simplicity and complexity, and you get to use a mouse! (Quite the upgrade, compared to Star Control 2). I'll fire this game up every now and then and just start from scratch because there's something satisfying about monopolizing the local coal mines and power stations. That's where my transport empire always starts: very lucrative, you see.
Transport Tycoon Deluxe is abandonware, a game so old no one is willing to put forth the effort to charge you for it anymore! That means you can download it free here. You can also check out an open source version of the game here.
Ever played TTD? Share your strategies for transport tycoonery in the comments!