I had to change blogs due to some personal issues so I lost my #1/2 rating with google and have been unable to really promote my blog until now. I am on a quest to get my rating back with my new blog but I have to say Entercard has been very helpful as well as my personal friends that have blogs and are willing to put my blog in their blog-roll. I don't know of any other free blog promoters but I am so willing to try them if they are out there and someone else has had success with them.
I belong to a whole bunch of social networking sites but haven't yet reseached and compared where the most traffic is coming from. I do know that a lot are coming from Twitter, though. I used to be very active in SU. Maybe I should check them out again.