Buy'n Sell Jewelry.com - http://www.buynselljewelry.com/
(FREE ADS FOR LIFE FOR BUYERS AND SELLERS OF JEWELRY! Simply register and begin adding your items for sale or wanted on the fastest growing FREE jewelry selling venue online!)
Ecrater - http://www.ecrater.com/ Sellers receive free website hosting, a free subdomain and a powerful tool to manage their free online stores. All products are posted to Google Product Search as well.
The sites that are familiar to many people for selling jewelry include:
Ebay - recently it is reported that the costs for ebay have gotten higher and higher. This may not be much of a problem because of the volumn of people that go to ebay.
Etsy - this site is for those who craft their own items. All items on Etsy must be handcrafted and sold by the artist. Etsy does not do much for you in the form of marketing, but this is something you can do for yourself with some time.
Ruby Lane - http://www.rubylane.com/ This site is less than Ebay but more than Etsy. Ruby Lane does more marketing for you than Etsy, but they do charge more to list. If you would rather do your own marketing this would not be your first choice.