Some of the useful Magento tools and references:

Magento Code Snippets

This GitHub page gives you a lot of very useful Magento Code Snippets

https://gist.github.com/arosenhagen/2397824

 

netz98 magerun CLI tools

The swiss army knife for Magento developers, sysadmins and devops. The tool provides a huge set of well tested command line commands which save hours of work time. All commands are extendable by a module API. http://magerun.net/

on GitHub: https://github.com/netz98/n98-magerun

Magento cards

A simple knowledge base for Magento development including code snippets, tips and tricks, commands, configurations and many more other topics.

https://makandracards.com/magento

Magento for Developers: Part 4—Magento Layouts, Blocks and Templates

The official dev guide for Magento 1.x

http://devdocs.magento.com/guides/m1x/magefordev/mage-for-dev-4.html