I can't rate this plugin highly enough.
If you're looking to setup a wordpress site and then add the functionality of ecommerce or just build a full on ecommerce site with an integrated blog - this is the best solution to your dreams.
Total freedom - totally customisable - bullet proof, smooth, easy and quick checkout process.
David the foxyshop wp plugin developer and the foxycart team are both very responsive to updating the code and adding new features. They tell it as it is and you don't need to become some genius php coder to tweak and design things up the way you want.
Everything else I've looked at to easily build a unique ecommerce site has been blown away by foxyshop and foxycart.