http://index.gl/ - The OpenGL Index
It's a searchable Index of all OpenGL functions and enums available in the new official XML based API-Registry with the only purpose of displaying the OpenGL version where the function/enum is available.
It shows OpenGL, OpenGL Core Profile and OpenGL ES. So if you are unsure in which OpenGL version, f.i. glUseProgram
was introduced - look no further! You've found the right place.
Currently there is no support for search for OpenGL-Extensions.
Additionally it would be nice to link to the reference pages. This is missing as well.
It is currently hosted run@cloudbees using their free option. So bandwidth might be limited and if the service is not used it goes into sleep mode which will add a little delay if it is accessed for the first time.
All the search capabilites are exposed in a simple HTTP-based API. So you don't have to use our little html/js based frontend.