Westwood's Red Alert was the first strategy game I ever bought.  It's easy-to-understand interface mixed with good gameplay make it very good for people just starting out in these types of games.  Although it doesn't have many units, Red Alert is still fun to play.  Its actually a very easy game to beat.  When I started out with it, I beat the computer the first time.  When I got TA about 6 months later, it took me about 3 tries before I could beat the computer.  Then I got Starcraft about 5 months after that and it took me a long time before I could even beat one computer.  Because Red Alert is easy to learn and fun to play, I think it is very good for a beginner at these types of games.