Brilliant Orange is fantastic, As well as How Football Explains the World. I've had The Ball is Round on my shelf for a while now, I need to start that. Bloody Confused by Chuck Culpepper is pretty interesting, but mainly for American readers (I think it has a different name in the UK), and I'll always love The Damned Utd.
Foul! by Andrew Jennings is a must, although slightly outdated as this point. And there's a Robert Enke book out I'd like to check out.