I heard good reviews about this ecommerce software. I am in the process of choosing an ecommerce package to power a site I am working on and I want to hear more opinions about this Magento. Other contenders would be X-cart, osCommerce, Zencart...any other?

You could try also Cubecart or Opencart...but it also depends on what do you want to achieve. Some carts are more complex than others...