Simple Debugging with WordPress – by Douglas Neiner, 3/16/10
Describes basic builtin debugging (i.e.)
Turn on debugging in wp-config.php
define( 'WP_DEBUG', true ) ;
define( 'WP_DEBUG_LOG', true ) ;
And how to leverage it a bit with some additional functionality.
Debugging WordPress Like a Master – by Bradvin, 9/26/10
Recommends NetBeans IDE (free) and xDebug. Describes setup process for local server.