The best TBS game in my opinion is the Age of Wonders series. I used to play Masters of Orion and Heroes of Might and Magic, but they are collecting dust now! Age of Wonders II: The Wizards Throne, by take2-interactive, is THE TBS-Fantasy. Check it out on www.ageofwonders2.com
A third release, named Shadow Magic is planned for september!
Enjoy playing!!