AFAIK, there's no
framework official/standard framework, and there will be as many plugin development styles as there are shades of white in north pole.
I'd say WordPress Coding Standards are a blueprint for a good style.
You'll find lots of good examples and excellent coders here in WPSE. A nice starting point: questions/tagged/plugin-development.
[ update, thanks to @Wyck contribution, a list of helper-plugins/boilerplates/frameworks ]
A set of useful classes for faster plugin development.
This is a plugin toolkit that helps developers write plugins faster. It consists of several classes which handle common tasks, such as generating settings pages, creating database tables and more.