I would like to know how I can export a material to let a friend use, without sending them a huge .blend file just to append the material from.
3 Answers
While its possible to invent some file-format to store Blender materials, this is currently not a common way to share materials.
Typically for this would be done by appending materials into a new Blend file, saving it, and sending this to a 3rd party.
In rare cases a material may depend on objects (using empties for mapping), in those cases you could create a group of objects in your Blend file and append that instead of the materials (the materials will load in too).
There is one option for cycles materials - Online Material Library. It is in the contrib addons that is normally included with non-release builds.
Primarily this addon provides access to a collection of materials but also has tools to import/export cycles node based materials to an xml-based text file that can easily be shared. While there was mention of adding support for BI materials there hasn't been any support added for them.
What you could do is put the material on a cube in the original file. Maybe pack the file if it includes images. Then copy-paste the cube to an empty blend file and share this. I think this would be about the minimal space requirement.