My vote goes to prestashop as its easier for new users and its free.For a better commercial version you can try Cs-cart.Magento needs long time to learn
Oscommerce is built on an outdated system - stay away Magento is what I would most recommend to anyone starting up an ecommmerce site... numerous reasons but basically it is the most professional solution for today's market Joomla with Virtuemart is great if you have a community based site. If you are just selling a couple items and don't need a full shopping cart then have a look into PayPal 'buy now' buttons. First build out your site in Wordpress or Modx and just add few lines of code and you're done! This is by far the easiest option out there.
There are some carts available for free,why can't you try go ogling it,and find solution for your cart for more functionalities and applications you have to pay for it,If you are need of free themes and templates can check me,