Creativity INC is one of the best books I have ever read on creativity and I have read a lot to know how much most of them really suck.
It has the added bonus of providing an alternative biography of Steve Jobs which in itself is interesting.
It's much more than a story about Pixar. It's a great insight into some of the very problems you deal with as you build and try to maintain a culture.
I can't recommend it enough.
If you want a peek into the books content Ed Catmul did a great talk at Standford.