CRAIGSLIST is number one. You can use a site like www.postlets.com to create very attractive flyers that fit into the craigslist layout smoothly and give a profesional style to it.
TIP - Remember to not just post it and forget about it, you need to update the posting at least once every week to bring it back to the top of the list.
TIP - Take really good pictures, try a wide angle lens and try to take pictures of the space (not whats in the space IE tables, toilets, clothing ect ect)
And if you dont get the response you are looking for call up a local real estate agent Because this is what we do full time and have the pipeline to bring tenants to landlords!
Hope this helped and best of luck!