Don't let the fact that these are free classified ads make you dismiss them as useless. Often the saying is true....you get what you pay for. With the internet, not so much. Depending on what your needs are and what you are trying to accomplish, free classified ads can be effective at delivering results.
There are all kinds of options for free classified ads. Some are a waste of time and others are so popular that it would be foolish not to try them. I know you have heard of Craigslists. It is a good place for many types of advertisements. That is not the only option for free classified ads though. There are a few other that I have used. US Free Ads and Oodle.com are good ones. But there are 1,000's more. Please don't waste time try to use them all!
There are also options for people who want to advertise brick and mortar established and start up businesses. Not that you can't use the free classified to promote those businesses but local advertising options provides a little more professionalism to the listing and has increased potential of getting noticed by the search engines. These focus on local listings or classifieds and it is where search is gets more specific primarily based on location.