Free Classified ads are a useful tool for a number of different occupations.
You may be offering/looking for a job or advertising and work from home opportunity. Free classified ads were one of my first ports of call when trying to get referrals for affiliate programmes. They are quick and easy to set up, they are free and most importantly of all they give RESULTS.
There are a zillion different free classified ad sites out there. To find them just type in Google 'Free classified ads' and there will be about 15 million results. My advice would be stick to the first page or so for the simple reason that those are the sites, that get the most traffic and so you ad will be seen the most with then. This does not mean you shouldn't post you ad on sites further down the search results but they will be less effective.
Don't forget to submit to the sponsored links at the top of the search results as well.
Free classified ads will not bring you immediate success, but they are a good place to start. I have never posted a blog ad on them but I post my affiliate links (only on the free classified ad sites where that is allowed).
Free classified ads are usually displayed in a similar way to a forum. They consist of a title, which is what the reader sees (rather like a topic title on a forum) and then the main body of the add (similar to the starting post in a forum, only the reader cannot always reply, unless you give your email address). I would recommend you write the body of your add in a text editor like Microsoft Word and then copy/paste it into the section; although keep it flexible because different free classified ad sites allow you different word limits.
You may want to advertise a few different affiliate links, in which case write your post/ad body for all of them first and post them all on the same site at once, rather than going through all the sites posting one ad and then doing it all again for another. This is because some of the sites you find, despite specifying 'free' in the search, will not be free, or you will not be allowed to submit your affiliate link; you will find yourself trying to post on a site where you already tried and failed with an earlier ad.