Craigslist.com, which is really Craigslist.org, offers one of the best free options for trying to fill a rental (whether it's single-family homes, townhouses, duplexes, condos and apartments). The biggest downside to Craigslist is the higher potential for Internet Scammers. Since the ads are free to post, anyone can go out and post spam ads with the hopes of scamming someone through Internet fraud.
One way around this though is to submit an ad on one of the Industry-leading rental websites and then create an ad on Craigslist to sync up with your rental ad. Why is this a good idea? First, Craigslist brings in over 50,000,000 unique visitors per month (where a high percentage of tenants only search for rentals on Craigslist). Secondly, by posting your rental on a paid Rental Website like Rental Househunter, you increase your trustworthiness as a Property Owner, since scammers are looking for those free ways to scam people.
In addition, most rental websites, like Rental Househunter, offer a way to track the number of renters who have viewed your ad. Craigslist does not provide this feature unfortunately, which means it will be hard to track the number of visitors you have received.