I use these on a daily basis and all the links are WordPress specific. Happy coding!
- Smashing Magazine
- Build Internet
- Dig WP
- CSS-Tricks
- WP Engineer
- Snipplr
- Paste Bin
- WordPress Support Forums
- WordPress Developer Documentation
- WordPress Plugin API
- WordPress Function Reference
- WordPress Filter/Hooks DB by Adam Brown
- WordPress PHPXref by Yoast
- WordPress StackExchange