If you are shopping around for a new shopping cart, I encourage you to take a serious look at E-Junkie.
I love the fact that you can use it with your existing website and it implements creative solutions to keep buyers focused thereby decreasing shopping cart abandonment.
I also like that you can sell actual product AND digital downloads in the same cart and it takes care of everything in the back end with the utmost professionalism. I have personally tested over 20 shopping carts, and I really like this one the best – especially since their services start at only $5/month and they have a free trial.