Yea Cart66 has been one of the big players for a while. If you look at that link I gave you'll see that the cart software falls into some general categories. Some of the cart solutions are total overkill for small set ups. For other situations you may have a very specific set of requirements. I live in NZ and many of the cart shipping solutions are all US-based, I needed a system where I could easily handle shipping from NZ and within NZ and after looking seriously at a lot of the carts most were deficient in this category and ruled themselves out from being able to be used "off-the-shelf".
I'd spend some time looking at the feature lists, thinking through your anticipated typical users purchase (from start to finish/delivery), and make sure there aren't any incompatibilities. They can be lengthy to set up if you have multiple products/categories and you don't want to invest time only to find it was wasted and need to start again.