Also- not an autobiography as such, but if you've not read The Damned United yet, it's well worth a look.
And that Brian Clough biog already mentioned.
I find that famous footballers' autobiographies tend to be spectacularly inane, with little to raise any genuine interest. I tend to steer clear.
The few genuinely good ones seem to be the lesser known types, like Garry Nelson, purely because they have more of a story to tell (and less of a...