The Citadel is an archive of information for George R.R. Martin's A Song of Ice and Fire.
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Jack Vance would head the list. Stephen King is up there. Bernard Cornwell, at least for his Sharpe's books. I like his new medieval series as well, but not the Civil War stuff. Whenever a new Flashman novel comes out I grab it right away. I watch for William Goldman's byline. And I confess to being addicted to Colleen McCullough's "First Man in Rome" series, despite the fact that she's an awful writer in some ways. Even so I find the books compulsively readable.
The Westeros network consists of several different sites, including a forum and a wiki, for all your A Song of Ice and Fire needs.