.edu and .gov backlinks are heavily weighted by Google, even though they will deny it. They're also very difficult to get. I found a little trick that lets you get legitimate .edu and .gov backlinks and it's so simple, I'm surprised I haven't seen this anywhere before.
Colleges and universities have blog sites for their professors, just like anywhere else. You can find them by going to Google and doing a search:
site:.edu inurl:blog "keyword relating to your website"
site:.gov inurl:blog "keyword relating to your website"
From there you just go to the sites you find and comment on the blog post, just like always. Most sites will let you add html tags in the comment body or at least in your name. The ones I've been using asked for a url and tagged my name automatically.
Be warned, though, the comments MUST be honest, content filled comments with no spam or promotion. You have to actually read the article and know what you're talking about in order to get the comment approved.
By doing this, you'll get some good, solid .edu and .gov backlinks and Google just eats that up.