David Byrne's Perfect City is well worth a read. He's been taking a folding bicycle on tour with him, and exploring the cities he visits. In the process, he's been thinking about what makes a perfect city. He seems to draw quite a bit a lot on Jane Jacobs' work.
I love this bit on density and why L.A. is so weird.
If a city doesn't have sufficient density, as in L.A., then strange things happen. It's human nature for us to look at one another— we're social animals after all. But when the urban situation causes the distance between us to increase and our interactions to be less frequent we have to use novel means to attract attention: big hair, skimpy clothes and plastic surgery. We become walking billboards.
(via Near Future Laboratory)