Github just added a new feature for users who dont use Gravatar, called Identicons.
GitHub is about to get a lot more colorful. Starting today, we are generating Identicons for anyone without a Gravatar. Our Identicons are simple 5×5 “pixel” sprites that are generated using a hash of the user’s ID. The algorithm walks through the hash and turns pixels on or off depending on even or odd values. These generated patterns, combined with hash-determined color values, ensures a huge number of unique Identicons.
Using a Gravatar but want to see what your identicon would be? Use this URL and replace my GitHub login with yours: