We've used Craigslist until they started charging for the ads. Our main problem with that venue is the quality of the applicants we receive. At $15.00 its still cheap, but I'm convinced that the people using Craigslist for looking for things are not the sharpest pencils in the box. It doesn't matter how many specific skills you desire an applicant to have or experience levels you require, nearly every unemployed person in your area will send you a resume.
We also own a rental property that has vacancies from time to time and its a rare prospect who doesn't ask some completely obvious or inane set of questions which the answers to are already in the listing.
Our best venue for advertising openings here has been Indeed.