When I was working for Trivadis  I have authored the Trivadis SQL & PL/SQL Guidelines. Those guidelines consists of a set of 91 rules that are explained along with good/bad coding examples.

The current version is 3.1.

Trivadis SQL & PL/SQL Coding Guidelines 3.1

For the earlier version of the guidelines (2.0) Philipp Salvisberg of Trivadis has written an PL/SQL Cop which checks PL/SQL and SQL code against the guidelines. Furthermore a ORACLE SQL Developer extension as well as a Sonar Plugin for the PLCop exist.

Both products may be purchased at Trivadis.