ShaderX
ATI Engineers contributed a number of chapters and sample code to the book ShaderX: Vertex and Pixel Shader Programming Tips and Tricks, edited by Wolfgang Engel. Now, all of these chapters are provided online for your reference.
ShaderX2
ATI has contributed a number of chapters and sample code to the books ShaderX2: Introductions and Tutorials with DirectX 9.0 and ShaderX2: Shader Programming Tips and Tricks With Directx 9.0, edited by Wolfgang Engel.
ShaderX3
ATI has contributed a number of chapters and sample code to the book ShaderX3: Advanced Rendering With DirectX And OpenGL from Charles River Media. A sample chapter from the book is available below.