World of Ice and Fire

The World of Ice and Fire is a companion to the Song of Ice and Fire series that began with A Game of Thrones. It's pure nerd-candy - a history of the world created for that series. It's written as though compiled by one of the maesters of Oldtown, so the reader is presented with the world from a Westerosi viewpoint and the biases that entails. It's very enjoyable, if you're a serious fan of the series - it details the history of each of the kingdoms that comprise the Seven Kingdoms of Westeros, as well as the Free Cities and other areas of Essos. There is a lot of detail in here not covered in the main series, and a few details that would reveal secrets in the main plot are coyly sidestepped (including one "we won't go into details here, because everyone knows this"). The illustrations are nicely done, and it adds a lot of depth to what is already a fantastically detailed world.