It seems like everyone and their brother is making an online store these days. While there are several good (free) shopping carts out there on the market, Volusion has taken the cake for me in the paid realm.
Volusion offers several levels of shopping cart capacity from 100 products to unlimited. They also offer a very comprehensive back-end with which to configure your store. It seems very overwhelming at first, but the software is very easy to use and can tell you quite a bit about your store and its customers.
There are several free templates available for you to use and they are very easy to edit as well. You can brand your store with your own logo that will also appear on your professional invoices and packing slips. Volusion is easily integrated with the major shipping companies, and it is especially easy to import your orders into UPS once you get the import template set up.
Personally I've set up 5 stores and helped on a couple others in the past 3 years. I urge you to give their free trial a try to see what it's all about. The forums are a very good place to learn how to do things and for connecting and sharing tips & tricks with other Volusion users.