4 of 6 Props to @scribu

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.

Highlighting:

Nowadays, I use Plugin Class Demo from @toscho as base for many plugins.

Right now, @Pippin is doing a series Introduction to WordPress Plugin Development 101 that may be of interest.

[ update, thanks to @Wyck contribution, a list of helper-plugins/boilerplates/frameworks ]

Plugin scbFramework, by @scribu:

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.

WordPress-Gear > PHP Boilerplate > Plugin stuff

  1. Plugin boilerplate by @tommcfarlin
  2. Object Oriented Plugin Template
  3. Settings framework by @gilbitron
  4. scbFramework - Classes for plugin dev
  5. WordPress Settings API - by @tareq_cse
  6. WP MVC - MVC framework to create plugins