Post your custom plugins for apps here. You can also join the awn-plugins project at http://code.google.com/p/awn-plugins, you will need a google account (its easy to setup).If you want to write plugins yourself, here's an incomplete tutorial demonstrating the Dbus interface.

Music Players:

Amarok Script
Amarok Script (little variation)
Audacious Script
Banshee Plugin
Exaile Plugin
Listen Plugin
Rhythmbox Plugin
Quodlibet Plugin

Chat Programs:

Xchat Plugin
Gaim Plugin
Pidgin Plugin
Gajim Patch

Downloads & Torrents:

KTorrent Plugin
Deluge Plugin
Firefox Downloads Plugin

Mail and Feed Readers:

Liferea Plugin
Evolution Plugin
Thunderbird extension

For developers, the Writing Plugins page may give some helpful hints. Be sure to notify the community of your efforts!