EDIT 09/24/2010: The GWJ Steam group for Civ V. It's public, so join away!
You may want to add the main manual download page on the official site:
Also the big fan sites for anyone not familiar with them:
Between those two, you could probably learn anything you wanted to know about any version of Civ.
Civilization V takes this definitive strategy game series in new directions with the introduction of hexagon tiles allowing for deeper strategy, more realistic gameplay and stunning organic landscapes for players to explore as they expand their empire. The brand new engine orchestrates a spectacular visual experience that brings players closer to the Civ experience than ever, featuring fully animated leaders interacting with players from a screen-filling diplomatic scene and speaking in their native language for the first time. Wars between empires feel massive as armies dominate the landscape, and combat is more exciting and intense than ever before. The addition of ranged bombardment allows players to fire weapons from behind the front lines, challenging players to develop clever new strategies to guarantee victory on the battlefield. In addition to the new gameplay features debuting in Civilization V, an extensive suite of community, modding and multiplayer elements will also make an appearance.
"Civilization V takes the franchise further by offering players a more immersive experience with deeper strategies; heightened tactical combat; vast, realistic landscapes to explore, battle over and claim as their own; and an in-game community hub where Civ fans can share content and compete against each other without leaving the game. This marks a new era that will forever change the franchise responsible for sleep deprivation and reduced productivity for nearly two decades."
Oh great, another Civ game to add to my pile of Civ games I want to play. :p
EDIT: Thanks to Peronthious on IRC for giving all of us the heads up.