For free sites, the choice would be chameleon link list submitter. Although traffic I'm getting right now is steadily increasing, it's not anywhere near enough to get consistent sales.
But as I said above, I don't think it's enough to use chameleon "as is". It needs to be augmented with your own sites and partners accounts.
I'll try and post some stats when I get a handle on how to add them up. I have to combine the webair control panel stats, google analytics, and awstats on hostgator. I'm trying to spread the bandwidth out so that all of my sites don't go down at once if I suddenly get a surge of traffic on a particular host.
