EnvReflection

 Takes a normal pass, a position pass and a latlong image, and outputs the environment reflection on the surface (either a latlong hdri, or a Nuke scene rendered through a spherical camera, or any made up latlong to create fake reflections). Figures out camera position from the normal's exr metadata.

Usage: Connect the node's three inputs as labeled. By default, the node will try to take the camera position (needed to figure out the reflection vector) from the metadata of its first input (normal pass). This only works for EXR's rendered using renderman. If no valid metadata is found, the node will show an error message.

Alternatively, you can change the 'camera' knob to 'use camera input'. When that option is selected, you can use the optional Camera input to plug you own camera and compute the reflections from its point of view.

There's additional controls to rotate the environment if needed.

Update (March 2011) - Added source code to downloads section. Feel free to use / modify / improve. Feedback and advice on how to improve the code is always welcome!