This is a Blackbody reference for emission materials. I have made it with Blender 2.69r59044. But if you are using Blender 2.68a, I have included the equivalent RGB node because you don't see the new Blackbody node.
There are 28 presets: Candle, Sunset, Sky Overcast, Daylight, Sun Noon, Blue Sky, etc. Also I have included a node group, called Bulb, which could be useful for lamps.
The model has been made by Robin Marin (@tuqueque). I have used the 2.61 bleder test version, but I have made some chages to show the emission materials better. You can download it here. It was created to test materials and it is a CC-BY lincensed blend.
You can see some renders and a brief explanation in my blog.