If you do not want to spend money you have to do some work. Try this common "google codes" to find some places for leaving backlinks.
site:.com inurl:blog "post a comment" -"comments closed" -"you must be logged in" "ADD YOUR KEYWORD"
site:.org inurl:blog "post a comment" -"comments closed" -"you must be logged in" "ADD YOUR KEYWORD"
site:.edu inurl:blog "post a comment" -"comments closed" -"you must be logged in" "ADD YOUR KEYWORD"
site:.gov inurl:blog "post a comment" -"comments closed" -"you must be logged in" "ADD YOUR KEYWORD"
site:.com "powered by expressionengine" "ADD YOUR KEYWORD"
site:.org "powered by expressionengine" "ADD YOUR KEYWORD"
site:.edu "powered by expressionengine" "ADD YOUR KEYWORD"
site:.gov "powered by expressionengine" "ADD YOUR KEYWORD"
site:.com ?Powered by BlogEngine.NET?site:.edu inurl:blog "post a comment" -"comments closed" -"you must be logged in" "ADD YOUR KEYWORD"
site:.org ?Powered by BlogEngine.NET?site:.edu inurl:blog "post a comment" -"comments closed" -"you must be logged in" "ADD YOUR KEYWORD"
site:.edu ?Powered by BlogEngine.NET?site:.edu inurl:blog "post a comment" -"comments closed" -"you must be logged in" "ADD YOUR KEYWORD"
site:.gov ?Powered by BlogEngine.NET?site:.edu inurl:blog "post a comment" -"comments closed" -"you must be logged in" "ADD YOUR KEYWORD"
The top four codes are designed to locate Wordpress blogs that allow for commenting. The middle group is designed to find Expression Engine blogs, and the bottom group is designed to find BlogEngine blogs
[FONT="]Expression Engine and BlogEngine are both popular among academics and some government agencies for some reason, which is why I like to focus on those in additional to Wordpress.[/FONT]