This patch adds a modest library of 26 common real-world materials and their index of refraction (IOR). A small button next to the material IOR slider lets users browse the presets and choose one. This was a feature request on the wiki.
There are a number of IOR preset tables found online, I compared two or three and selected likely materials for Blender projects. I used median values for those materials which have varying density in nature.
A more elaborate patch could keep these in a resource file but I think most users just want a few basic materials without resorting to Google every time.
(The attached patch has incorrect line numbers and probably cannot be applied to CVS directly, though it is just a few lines and can be applied with an editor by reading the patch text. This is because I have made several patches on other features for this particular file, which are still in the queue, and I did not bother to create a whole new sandbox for each new feature.)