Good simulation games like OpenTTD?
I like simulation games, but I'm having a hard time to find good ones. There are a bunch of games like Trade Nation or Bug Village, but they are not what I called true simulation games. They all do the same things and it takes several days if not weeks just to get it a bit interesting... And even then it's a "Wait 8 hours to build" over and over again...
I already have OpenTTD (Transport Tycoon clone) and Civilization which are just great. Any suggestions for good simulations games like those?