The Wildwater Racing manual is an online resource containing very useful information. It is put together from input from the national coaches, and continues to evolve.
The new BCU star awards provide a great framework to improve on your understanding and skills to allow you to perform better and enjoy yourself more.
The Danger Zone book, available in a chapter by chapter PDF download from USA, is a great resource and possibly still the best book written about Wildwater Racing. Although it is some 20 years plus old - large sections are still very relevant - particularly the physiology and case studies.
The rivers FAQ will suggest some rivers, depending upon your skill level.