I have found there is no one “great” plugin that works for any (or even most) eCommerce needs with WordPress.
Some of the big ones:
http://www.instinct.co.nz/e-commerce/ – paid – free version is severley handicapped
http://cart66.com/ – paid – haven’t tried this one, but seen others use it. It recently changed its name from something else. I think it was like PHPurchase or something like that.
http://shopplugin.net/ – again, the paid version makes the most sense, but its not right for everyone.
What I’d suggest is installing as many as you can one at a time and see what fits your needs the best. Everyone has different points of interest
