There are many free methods like Article Marketing, Forums, Blogs etc. Which one has been most productive for you? If a combination of paid and free methods is to be be suggested which one do you feel is the best?
Link exchanges work well for me. I get nice search engine traffic and predicted PR5 just from link exchanges. You can read about it in my Case Study.
For me social bookmarking, blogging, forum postings, directories... These methods really works for me