OpenJPA Manuals:

• openjpa-0.9.0-incubating: full HTML manual javadocs

Project Resource

The OpenJPA Wiki has information on running OpenJPA, as well as checking out and building from source, and many other things.

Books

A number of books covering OpenJPA are planned or in production. Books About OpenJPA

Articles and Interviews

TheServerSide.com discussion on OpenJPA and Java EE 5