Age of Empires II under Virtual PC
This is a great game, but if you needed me to tell you that then I do not know where you have been. Released in 1999 this game has been heralded as one of the greatest real-time strategy games of all times. AoEII has many of the elements common to most real time strategy games, you have to build armies and buildings to both defend yourself and achieve specific goals, while having to balance resources at all times.
The real innovation in Age of Empires was the concept of "ages". As you progressed through each mission you could move your nation from the Dark Ages to the Feudal Age, then the Castle Age and finally the Imperial Age. Moving to the next age requires a significant amount of resource. But it means that you will have access to more advanced buildings and units (though these units will in turn cost more, so more resource management is needed).
Age of Empires II runs perfectly under Virtual PC - as it should, because this game is actually one of the few games that we formally test. Age of Empires II gets tested under Virtual PC to ensure that we are correctly handling copy-protected CDs, like the one used by this game.
If you have never played this game - go out and get it know (you should be able to find it for ~$10) and have some fun.