Looking for a good starting place for creating shaders for the new OpenGL ES 2.0 available on the iPhone 3Gs?
The orange book has an online home that's well worth looking at. The Orange Book (the current version of which actually has more purple than orange) is the official book on the shading language. If you're thinking of writing shaders, this is the first resource you should get. The official site has example shaders and links plus errata, so you might want to bookmark it.
You should also check out this page, which has lots of shader resources, including a zip full of shaders that you can use.
Lastly, in the Developer folder on your hard drive, in /Applications/Graphics Tools, there's a program called OpenGL Shader Builder that you might want to check out.