If your looking for good RTS games.
Warcraft III Reign of Chaos
Warcraft III Frozen Throne
Sins of a Solar Empire?
Command and Conquer: Tiberian Wars?
World in Conflict?
Lord of the Rings Battle for Middle Earth is quite addicting so I have heard also.
I know that Warcraft III is just good ole fashion, non complex great fun with great stories! The RTS aspect of it is easy to learn and does not require a lot of Micromanaging to be good at, but will take time to become great. You can also play on Battlenet in ranked ladder games where you can gain rank, and play a multitude of different game type with balanced races.
If you want a bit more turn based style CIV 4 style there is :
Heroes of Might and Magic V
*WAY OLDSCHOOL* Heroes of Might and Magic III
I still to this day play Heroes of Might and Magic III, it is just way too much fun, and can run on any computer you throw at it post 1998. Great mix of some city building, hero building, and great chess like battles involving strategy and magic, with very difficult AI if you like, although there is 5 settings.
Heroes of Might and Magic V is the modern day version of III with much better graphics, but of course is a little different.
Hope this helps you out

Again if you like Age of Empires - I think you would love Warcraft III