Python debugging
 * use Web2Py shell: http://www.vimeo.com/879939
 * http://docs.python.org/library/doctest.html
 * http://docs.python.org/library/bdb.html

CSS & Javascript debugging
 * use Firebug: http://code.google.com/support/bin/answer.py?answer=77412&topic=12044

jQuery:
 * http://www.tvidesign.co.uk/blog/improve-your-jquery-25-excellent-tips.aspx

Ext:
 * http://extjs.com/learn/Tutorial:Introduction_to_Ext_2.0
 * http://extjs.com/learn/Manual:Basic_Application_Design
 * http://extjs.com/forum/showthread.php?t=26728
 * http://extjs.com/learn/Ext_FAQ_Debugging