2k Games: Civilization IV:Official support site. Includes technical support FAQs, developer blog, comparisons against previous games in the series, modifications, and downloads.
1 Big Community: Civilization Forums: Discussion forums covering Civilization III and IV strategy, multiplayer and modding/customization.
1UP: Preview, by Garnett Lee: "...we were convinced this new Civilization was right in line to follow in the footsteps of its older siblings."
3D Gamers: Includes information, news, screenshots, and downloads.
Apolyton.net: Civ IV: News, screenshots and discussion forums covering strategy, multiplayer and democracy games.
Civilization Fanatics' Center: Civ IV: Discussion forums covering game strategy, customization and technical support. Also offers articles, technology tree and hall of fame.
GameSpot: Offers previews, news, screenshots, movies, and links.
GameSpy: News, previews, screenshots, and a movie.
IGN: Previews, press releases, news, screenshots, and videos.
The Atlas Project: Alternative random map generator software. Includes manual, downloads, screenshots and release history.