This one's getting a little tougher and maybe over-used due to excessive usage by SEOers.

First, Wordpress MU...The "MU" stands for "multi user" and it's a Wordpress plug in that allows the owner of a blog to give away free WP blogs, in essence making the owner a little like Blogger.com.

So if you can find WPMU sites, you'll be able to create a blog of your own for free.

Here's some fingerprints you can try to find WPMU blogs:

"you'll be blogging seconds later"

"you'll be blogging seconds later" + "keywords"

inurl:wp-signup.php

inurl:wp-signup.php + "Must be at least 4 characters"

Find some fingerprints of your own, so your network of WPMU blogs is different than others.

Also, don't spam these sites...WPMU blogs are good for using PLR content, etc. Put up something decent and relevant, it doesn't have to be original. Just make it good enough to pass a human inspection.