The makers of Runtime Revolution.
Their website has lots of information on it for both new users as well as seasoned users.
Components, Stacks, Tools and Resources for Runtime Revolution, all made with 100% revTalk goodness.
A large set of tutorials created by Rev experts to teach you how to work with Revolution from the ground up. These were created over several months and presented live in conference. Each stack teaches you a critical concept and provides examples, scripts, and sample stacks to get you up to speed. Start at the beginning and work your way through in order and you'll be an expert too.
Websize for and by the Rev developer community.
A variety of developer resources, including tutorials and articles for both beginners and pros. How to set up old-style CGIs, how to handle "send in time" instead of using inefficient repeat loops, functions explained, how to test your stacks, and lots more.
For HyperCard converts, a step-by-step tutorial on how to convert your stacks to Revolution, including some of the main pitfalls to avoid and differences to attend to.