There are lots of people out there making lots of money selling their unwanted items, and other things, through online auction houses such as e-bay. 

Online Auction Strategies is a great place to learn the basics from an accomplished e-bay seller.  There is information on everything from where to get your products, to pricing and writing your ad.  If you don't want to read the tips in order, check out his menu page.

The Auction Chick also has some great tips and ideas.

You can also get great info from the OnLine Auction Sellers Association site.