I found blog commenting works great, but for some reason or another (maybe too many in one day caused a spike that google notices or what not) my sites rankings drop for a couple of weeks after I post a few, so what I've learned is space them out and make sure that you are continuous so it is more natural progression to google. I don't do it anymore for a couple of reasons, but I have seen it work. I like submissions to social media sites, and social book marking sites a lot though, the no-follow tag doesn't seem to stop google from spreading you at least a little link love.