The new civilization IV: Beyond the sword expansion is coming soon. In preparation I played a few games of Civ IV warlords again and I must say, it’s still very good. Beyond the swords will add a lot of nice new features. Especially the corporations and improved new AI sounds good. I preordered my copy from gameplay.co.uk, and it’s usually delivered around the official release date.

Civfanatics - Excellent site with a load of information and a great forum
Beyond the sword – Official site
** UPDATE **
A very nice history and an interview can be found at Gamasutra