Here are a bunch of places to post free ads. These are only some of them, and I will try to add more from time to time. If you run a free ads forum or a free classifieds site and want me to list here, leave me a note in the comments.
Forums
Free Ads Planet <— Our forum, post your ads there!
Free Advertising Classified Ads
The Free Advertising Site
Post Free Ads Forum
Free-Adverts
Free Ads Board
Free To Advertise Forum
Free Advertising Zone
Post Your Ad
The Free Ad Forum
Free AdvertisingForum
Free Forum Ads
Classifieds
Craigslist
Classifieds for Free
USFreeads
InetGiant
Stumblehere Classifieds
Yahoo Classifieds
Free Ads City