I can only think of adbrite and infolnks at this stage. All others I have used require you to "add funds" before an ad is run.
soclial bookmark are worthless then ever.... i prefer do my own way get an .edu domain , post your article related you niche , that one point to your niche with 3 outbound dofollow - trackback backlinks , then ping - blog comment that point to your .edu domain , the same static page article that point to you home page with the 3 dofollo backlinks, so you'll have the bcklinks just from High PR websites That one google loves .EDU , your will never get banned from backlinks blasting or deindex . any many more fetures plus if then you create a little php lines into your domain index that can create around 50k - 100k unique visits by day just with some good footprint Cheers EaSy7