I just completed a spur of the moment re-read of Use of Weapons by Ian M. Banks.
Such a great book, even better the second (or third?) time around. The Culture series has probably always been my most beloved science-fiction universe, but I think that this book stands out even amongst its peers. The Culture series has always explored the duality between utopia and its associated costs, but I think this book best exemplifies the callousness and cruelty that the Culture is capable of employing - indeed it is not just about the use of weapons by our dark, devious and utterly damaged mercenary protagonist, but also about he himself is used as a weapon in the incomprehensible games of AI Minds.
The clever interweaving narratives moving both forwards and backwards in time, builds to devastating conclusion. But despite the fact whole chapters of the novel take place chronologically after the climax of the narrative, I remember being shocked and surprised by the ending on my first read through. The Chair and The Chairmaker will haunt my dreams tonight.
Side note: I really need to do an RP set in the Culture Universe, would be fucking sick.