General Civ Sites

 Realms Beyond, home to a lot of friendly and like-minded Civilization players, and host of the Civilization Epics tournament

 CivFanatics: Information about the Civ series and home of lots of succession games (located in their stories & tales forums)

 Official Civ IV site from Firaxis/2K Games

Civ IV Game Report Sites

 Sirian's Writings: Sirian is the main organizer of the RB Epics tournament, and also hosts a lot of great game reports

 Sulla's Civ 4 Site, hosting a complete walkthrough and, in the future, more game reports

 Snaproll's Civilization 4 Site, featuring reports of private, PBEM and tournament games

 Speaker for the Dead, another site with game reports for both Civ 3 and 4