Good bathroom reading.
The built-in documentation for the Go standard library.
The built-in documentation for the Go tools.
The official Go Language specification.
The documentation for Google App Engine's Go runtime.
A summary of the changes between Go releases.
A document that specifies the conditions under which reads of a variable in one goroutine can be guaranteed to observe values produced by writes to the same variable in a different goroutine.
Using GDB to debug Go programs.