FatFreeCart - Free shopping cart for Google Checkout and PayPal <-- Free, limited functions, integrates with PayPal
E-junkie Shopping Cart for selling downloads & tangible goods <-- Subscriptions apply ($5/month), a lot more features, integrates with PayPal.

I use the free version on my sites now and really like the handling of the cart. No problems at all. I did have to edit every one of my existing cart scripts, but well worth it - PayPal's cart is not really cross-browser friendly and FatFree Cart fixed all the existing PayPal bugs.

I'm in the process of building a jewelry site of my own, and will be using osCommerce for that due to the amount of items (I don't want to code pages for all 900+ items). osCommerce is good, but is not very webmaster friendly and is somewhat of a pain to change the design of its cookie-cutter looks.