Greyhawk is strikingly simmilar to the Forgotten Realms, the only difference being the histories, characters, and geography. Both are also near perfect replicas of the generic world introduced in the Player's Handbook.
There are countless books out from this series. Gary Gygax is an influential writer, and he has written the books that define this world's history. This is the only AD&D world based on books. (Dark Sun was greatly changed by the Prism Pentad, which, it could be said, wrote the history of Athas, where the boxed set had given no history at all. But, the world of the Dark Sun was around before this pentad.)
This once-popular world seems not to hold the intrest of HTML know-hows; there are no Greyhawk sites registered in Altavista or Yahoo. If you have found a good Greyhawk site, please tell me.