Craigslist - Humboldt - Quick and easy to use.
ebay - The world's online marketplace.
KMUD class ads - If you miss it on the radio you can view the ads here anytime. They are in the "community" section.
The Trader - Based in Southern Humboldt, serving Humboldt, Trinity, Del Norte, Mendocino, and Lake Counties.
Tri-City Weekly - Humboldt County classifieds.
