Here is a list of 36 top classified ads where people actually view, post ads and buy stuff. They have eliminated all junk sites from this list. There's no ffa pages, forums acting like classified sites,classified sites which are filled with spam or which have no traffic and are not well maintained. These are actual classified ads site where in case you post your commercial you actually have a serious chance of somebody seeing your commercial and responding. There's no sites here with an Alexa rating over 150,000. This means that the sites below all get serious traffic.
1. www.craigslist.org The grandaddy of classified ads sites.
2. www.backpage.com The second busiest classified site after Craigslist. This is where all the escort ads went after Craigslist took down their erotic ads section due to pressure from 17 Attorney Generals. Not so with Village Voice owned Backpage.com. They told the attorney generals they were just fine with their erotic ads section thank you. Those guys at the Village Voice have major cohones.
3. www.gumtree.com Weird name but this site is one of the busiest classifieds sites out there. This high traffic classifieds site is focused on UK ads.
4. www.oodle.com This serious classified site has partnerships with ForRent.com in the US and Autotrader UK.
5. www.ebayclassifieds.com The official classifieds site for Ebay.
6. www.olx.com This board has a presence in most countries and can be read in English or Spanish.
7. www.usfreeads.com A popular US focused site with a large business opportunity and pet section.
8. www.classifiedads.com Classifieds focused on the English speaking world. US, UK, AU, and India.
9. http://www.inetgiant.com A green board not only in color but in their ads. They have a well represented area for green products. The board is pretty much translated in most languages. I checked their Lithuanian board. No ads there yet. Do you want to be the first?
10. www.adpost.com Solid board with presences in the United States, Singapore,Canada,Malaysia, United Kingdom, Philippines, Ireland, Australia, India, Indonesia, New Zealand and Hong Kong.