I decided to learn some OpenGL ES 2.0 and I am trying to pick a practice platform for it. What comes to possible target platform, it could be Android, iPhone or WebGL. But I don't want to spend too much time and effort to get the environment setup properly.
Would you recommend WebGL for a fast start to OpenGL ES 2.0 learning or something else?
Edit: I am using Mac and I am not really interested in ES 1.x at the moment.
If you register as a developer at the iOS Developer Center (free), you can download Xcode and the iOS SDK (again, for free when you get Xcode 3), which includes a simulator capable of OpenGL ES 2.0. This of course assumes you have a Mac to run that all on.
Once you have the SDK, you can simply start up Xcode and create a new application based on the OpenGL ES Application template. This application will be a fully functional OpenGL ES 1.1 and 2.0 iOS application that you can build and run in the simulator. You can ignore all of the iOS-specific setup code and focus on the -drawFrame method in the xxxViewController.m class, which is where the OpenGL ES 2.0 drawing code lies.
This can be a pretty quick environment to set up for playing with OpenGL ES 2.0 shaders. I've also tried out the PowerVR SDK package that trenki suggests, and it is a little more involved to get something set up with that. If you're on Windows, it will be a lot more viable of a solution than the Mac-based iOS SDK I describe here.
One other shader development tool that can come in handy for prototyping on the Mac is Quartz Composer. It comes along with Xcode, and provides a visual prototyping environment for all sorts of effects, including OpenGL shaders. I demonstrate an example of doing this kind of prototyping in an article I wrote here. Desktop GLSL and the implementation in OpenGL ES differs slightly, but much is the same between the two.
While targeted at iOS, I taught a class on OpenGL ES 2.0 recently as part of a course that can be downloaded from iTunes U for free. It might helpful in getting up to speed on shaders.