Call of duty 5 is going to be the fifth addition to the Call of Duty series, or 8 if you include all the current expansion packs and any console versions.
The news of this new addition was confirmed on December 2, 2007. The expexted release date is sometime around March 31 2009 which is the end of Activision's fiscal year. The game will be available on the following platforms: XBOX 360, Wii, Playstation 3, Playstation 2 and PC.

This video gives an insight to the sort of tactics needed in Call of Duty 5: World at War.