I've searched through the stack exchange for wordpress and was unable to come up with an answer to this question. All of the wordpress codex's examples and external resources come from 2004-2006. I'd love an example of a popular Wordpress plugin that is also well-written. As I'm fairly new to programming (less than 1 year in), this would be immensely helpful.
You can buy the Professional WordPress Plugin Development book from Amazon: http://www.amazon.com/Professional-WordPress-Plugin-Development-Williams/dp/0470916222 I'm learning tons from it and it's packed full of good information about best practices. It will walk you through building your own plugin with lots of code samples. I cannot recommend it enough. If you're serious about learning to write plugins then this is one book you absolutely must buy.
Take a look at the highest voted Qs on WPSE