Yeah have to agree with interman aswell. Chris Sawyers Transport Tycoon Deluxe Edition or Locomotion are excellent. Rollercoaster tycoon 1 and 2 are also notable, however no3 in the series is 3D which ditracts from the gameplay somewhat.

The latest Sim City is going cheap aswell, however it is a really in-depth management system which can get a bit too much if you are used to Chris Sawyer's type of sim.