Recommend good hacker / security books?

I am currently writing a lot of software with public interfaces, and I would like to know more about how hackers break into systems, and the best ways to prevent them. I understand basic DoS and dictionary attacks, and I use bound variables for database queries, but that's all pretty basic. What are some good books for server side security?

Did you try the articles and missions on http://www.hackthissite.org/ ?
On that site I learnt a lot about how not to build my sites.