Blog commenting
Classified (eg CL)
Q&As (eg yahoo answers, quora, etc...)
Pinterest
FB group/fan page posting
YT comments
Forum posts
In all cases, the key is to post quality content/posts. Forget about posting one liners such as "OMG you have to check this out www.yourafflink.com"; you'll get banned in a second and even if you didn't, you won't get any sales. You have to write a useful, informative paragraph, and then only insert your link as naturally as possible, avoiding the hard sell approach at all costs.
Moreover, as posters above have already noted, free methods aren't 'free' - you are investing your time (and you'll need to invest considerable amount of time to make serious money with free methods). How about you find a part-time job offline, save some money, then invest in an MNS + SEO + Paid Traffic?
Mancar