I use roman cart and osCommence and both have there better fetures.
Romancart.com
It is a kinda software on the web were you can add prodocts to there product manerger and have links to your own shopping cart. The product manager lets you make a code in html which you add to any webpage.
Romancart costs from free to $369.99 per year.
osCommence.com
oscommence is free and it is a php and db program which allow you to add products and you have to use there website setup to make the e-commerce part of the site.
You need to do some reseach before you deside and if you need any questions answered add me on msn or yahoo.