What are your favorite PostgreSQL performance resources?

If you were to gird up your loins and learn PostgreSQL performance optimization from scratch, but already knowing where to find the articles and manuals and stuff online, what URLs would you be visiting? What core bits of PostgreSQL would you focus on understanding the most deeply? What books would you buy?

Note: if your comment doesn’t appear it probably went into the spam queue because of links. I’ll retrieve it, don’t worry.

Note: VividCortex is the startup I founded in 2012. It’s the easiest way to monitor what your servers are doing in production. VividCortex offers MySQL performance monitoring and PostgreSQL performance management among many other features.