Esri on GitHub
There are quite a few code samples available from Esri, but they are somewhat scattered around the Esri Resource Center. Now Esri is starting to share many of these resources on GitHub where you can access these resources.
If you are familiar with any of the ArcGIS for specific industry vertical initiatives, these resources are in the process of being made available here. Stay tuned to this location as the Esri DevSummit approaches.