My personal favorite is comersus.com, it has a paid and a free edition. Try out the free edition first, it is fantastic! The paid or Power addition has a lot of other power features.
I would say it depends on your needs. Also, price could be a factor, some I received quotes from were $16,000 for a small business, and that was out of reach for what I was doing at the time. If you are selling just a few different items, a free cart like oscommerce should be great.