The Citadel is an archive of information for George R.R. Martin's A Song of Ice and Fire.
New to the series? Read our spoiler-free review of A Game of Thrones.
Mr. Martin has read several chapters that will appear in A Dance with Dragons (Amazon: US, UK), and reports on a number of them can be found in this forum. Please note that this forum, and in particular the chapter report topics, contain a lot of spoilers. Some of the recent contributions to the So Spake Martin collection (both emails as well as chats & interviews) also contain information about the next book.
The Westeros network consists of several different sites, including a forum and a wiki, for all your A Song of Ice and Fire needs.