I’ve found that one of the best ways to learn and improve upon writing plugins for WordPress is to review, learn from, and emulate the coding styles and best practices of really good WordPress Developers.
As a community post and a personal resource I’ll list here some WordPress Developers that produce popular, well written, and extremely useful plugins for the WordPress plugin community. Simply reviewing the plugins from this list of developers can go a long way in helping improve your own plugin writing.
Alex M. (Viper007Bond)
(You can find my personal blog at Viper007Bond.com) I work for Automattic (the company behind WordPress.com) doing VIP support and coding up random things. As you may notice below, I like writing WordPress plugins and can’t help writing more. I also contribute to the WordPress core from time to time. My most recent major contribution was the native embeds feature.
I like WordPress. A lot. My base of operations is my personal blog, which is where you’ll find a lot of neat stuff about WordPress. Oh, and I run this neat community called Theme Hybrid. That’s where you’ll find my WordPress-theme stuff.
Joost de Valk (Yoast)
I’m a WordPress / web developer, SEO and online marketer. Throughout my career I’ve worked at several companies, ranging from enterprise hosting to online marketing agencies, allowing me to work with several large businesses around the world, ranging from Dutch leaders as KPN and KLM to world leaders as eBay, RTL and Salesforce. I now work as a freelance consultant and developer, mostly working on large scale sites. If you want to know more, visit my homepage, follow me on Twitter or check my Google+ Profile.
This is of course very small and incomplete list of professional WordPress plugin developers. They are the authors of plugins I’ve personally used and have looked at therefore they make the list. Please feel free to send through comments WordPress plugin authors that you would also like to see on this list.
There’s also a couple fun pages showing the top WordPress plugin authors: