RESTful APIs

• Swagger at http://swagger.io/
• Apiary Blueprint at http://apiary.io
• RAML at http://raml.org/

Resources with best practices and principles for API design:

• Top 12 Best Practices for RESTful API Architecture (bacancytechnology.com)
• Best Practices for Designing a Pragmatic RESTful API | Vinay Sahni
• 10 Best Practices for Better RESTful API | by M-Way Solutions | Medium
• RESTFul API Guidelines (apistylebook.com)
• Microsoft REST API Guidelines Are Not RESTful (infoq.com)
• Principles of good RESTful API Design – Code Planet (wordpress.com)

• A Few Great Ways to Consume RESTful API in C# - Code Maze (code-maze.com)

Authentication options for APIs

• rest - RESTful Authentication - Stack Overflow
• Authentication for REST web services - Stack Overflow
• Knowledge Sharing...: Shared Key Authentication [Good option to consider implementing auth in REST service] (anuchandy.blogspot.com)
• Authentication to a RESTful web service in an AngularJS web app | Bruno Scopelliti