NewsBlur extension for Opera.
http://addons.opera.com/extensions/details/newsblur-notifier/
The latest published version can now be always be found at addons.opera.com. Installing it from there will keep it auto-updated whenever a new version is released.
For development just drag and drop the config.xml into your Opera window to install it in developer mode. The button should appear on the toolbar if successful. Right click -> Preferences to set options.