Cart66 is a great shopping cart plugin for WordPress which works great for smaller and medium websites.
Another popular plugin is Woocommerce which is worth trying. My favorite remains Cart66 since is not buggy and has great support in case something doesn’t work properly.
Lemonstand Shopping Cart is a dedicated powerful and flexible ecommerce platform which makes it a great solution for medium to large websites. If you’re serious about selling products online this is the way to go.
While ultimately all eCommerce platforms enable sales, reviewing your business goals will help you select the best solution with the best return of investment.