Shopping Carts
I like CityMax.com for online stores. For the basic fee of $20 per month they give you a ton of options including a nice shopping cart, password protected pages, polls, etc. CityMax is actually an entire website building and hosting service. Their shopping cart automatically updates UPS rates; you just have to enter the weight of your products. It automatically figures sales taxes. You can build your website as a test for free.
GoDaddy.com also has a shopping cart feature they can easily add to their hosted websites.