You can use any of the local classified website to submit your ad. Gumtree or Adlandpro are good and you can try them.
You can search free classifieds ads listing , choose right category for your posting and post your ad there.
Craiglist
Well,
For car ads, local classified, yellow pages and local news papers are the best one, by the way craiglist is having local city ads too. You can list according to your nearest city.
Thanks
Try http://www.tatzo.com 100% Free
Craigslist ( http://craigslist.com )
Vendalism ( http://vendalism.com ) - if you make a listing here it will also post your ad on craigslist for you
Kijiji ( http://kijiji.com )
What is a good website where I can post a car for free that I am selling that has any states in the United States where I can post by ad for FREE? Example: Car Daddy.com