Social bookmarking using submitterbot. Although they have article and directory submission, I find bookmarking submission more effective than the other two.
although I obviously have a vested interest, the easiest way to build backlinks that count is autoblogging. It beats other methods because the autoblogs keep adding backlinks come rain, come snow, so eventually *you will rank for the terms you want*
I use tnx.net if anybody wants to join pm for invitation code and you will receive 1000 free points which is good for renting few PR links for a month or a hundred of 0 PR links if you wish.