[wp-hackers] advanced plugin development for wordpress

[Mayur somani]

Hi
I can do all the basic stuff on plugin development and have gone through the
codex thoroughly.
Can somebody please provide me resources and links on advanced stuff on
plugin development.

Generally I get the advice that read the sources of other plugins.
So please provide the names of best wordpress plugins till date (from coding
perspective) so that I can learn something from their sources.

Thank you for your time.

-Mayur