This page is getting worked on.
I think Total Annihilation is one whooping game. Made game of the year 1997. It's got some of the greatest 3d graphics I've seen for a strategy game and some nice music. The AI needs work though and it has some sloppy programming (they're up to patch 3.1 now).
Of course new games constantly come out and outshine the old games but there are add-ons to it like Core Contingency and Battle Tactics. Core Contingency is a great add-on, giving you a new wide range of units to use and annihilate your enemy.

NEWS: Well Cavedog has been disbanded so all TA related sponsored stuff has stuff. It's really a shame, TA was such a great game.

Info about Total Annihilation at these links:

The place where it happens
The creators
Great TA site for 3rd party stuff, etc.