Lots of good suggestions here. I've just ordered Anne Leckie's 'ancillary' trilogy.

I'll recommend Gene Wolfe's Book of the New Sun (The Shadow of the Torturer, The Claw of the Conciliator, The Sword of the Lictor and The Citadel of the Autarch) - Lots of weird, cool imagery and ideas.

I need to get around to The Urth of the New Sun at some point.