Free PostgreSQL Resources
You'll have to give up an email address and register to download the free pdf postgre book from this site.
This looks like a fairly comprehensive site.
PostgreSQL Mirror Sites
Download the latest versino of PostgreSQL.
PostgreSQL Technical Documentation
Articles and reference materials.
PostgreSQL JDBC Drivers
From here you will get up to date information relating to the JDBC driver for PostgreSQL, download pre-compiled driver in a jar file, and look at current documentation
Professional Linux Programming Part 1 - Accessing PostgreSQL from Code
Mostly C programming examples.