http://developer.amd.com/tools-and-sdks/heterogeneous-comput...
The Khronos website has a huge page with a list of OpenCL tutorials and books:
https://www.khronos.org/opencl/resources
Amazon has a number of OpenCL books available:
* http://www.amazon.com/OpenCL-Action-Accelerate-Graphics-Comp...
* http://www.amazon.com/Heterogeneous-Computing-OpenCL-Second-...
* http://www.amazon.com/OpenCL-Programming-Guide-Aaftab-Munshi...
This book is available on Amazon but the previous edition is available for free:
http://www.fixstars.com/en/opencl/book/
Intel's website also has some "Getting Started" articles and optimization guides for OpenCL (for CPU, GPU, and Xeon Phi):