These are some of my favorite sites to buy/sell homeschool curriculum. Each has a link to the site and then my user ID in () so you can look up my stuff too, if applicable. EnJOY and spread the news around.
Homeschool Classifieds (joycorner)
Edify at Home (Joy Corner/5forJesus)
eBay(5forjesus)
Veg Source
HSLDA Curriculum Market

You can also try looking up Yahoo groups for your specific wants/needs. There is one for ACE School of  Tomorrow, Saxon Math, Math-u-See, Sonlight to name a few.