[bduerst]

Player of Games is the second book, and the one I recommend people start The Culture series with.

The first book Consider Phlebas isn't bad, but it isn't as well developed as the rest of the series IMO.

[hesperiidae]

It's a great starting point, since not only is the story both fun and interesting, but it also shows what the Culture's values and methods are in a very satisfying way by juxtaposing them against the Empire through the tournaments of the latter's own game.