Say your niche is the iPhone. Type "iphone forums" into google. You will now see pages and pages of iPhone forums. Much like Angelas and Pauls links go through the forums registering and leaving your backlinks in the signature. I know this is nothing new but thought I would post it as an idea for anyone who didn't think to do it. It's an easy way to get some good backlinks and is pretty limitless! To speed things up use Roboform!