Free sites on which to advertise

Where can I find free sites on which to advertise?

A simple Web search using any of the major search engines will yield a listing of free ad sites. Use search terms, such as "free business classifieds," "paid business classifieds," "pay per click search engines," "free and paid safelists," etc. Be sure to use more than one search engine, as results may vary from engine to engine. Also, use variations on search terms to find lesser-known, but still valuable advertising sites.