Just created a small blog post about Identicons and how you can create some for your users instead of default profile images. An Identicon is a visual representation of a hash value, usually of an IP address, that serves to identify a user. Much like we know from github, wordpress and other sites.
With few lines of code you could implement it on your own projects.
Shared code in the blog post and a small form, so you can try to create one and see the result.