Shopping cart

Hi our site is using ejunkie for our cart but we have run into way to many limitations with their system in terms of discounts and such. Our site is built so each product has its own themes background and ejunkie allows this to happen since the code for each product is just paced with html. Are there any other cart systems that work with wordpress that don’t require the same background to be used for every product page and also have discount options such as buy 1 get one.