I’ve almost used this a couple of times, but at the last minute the projects have fallen through.
Fairly simple to install, setup and use open source shopping cart software, which seems to be the most popular of its kind out there.
I looked at a few different options and so far osCommerce looks to be the best by far.
http://www.mals-e.com/home.php
Ok, so the thing I really like about this is that you get access to a free SSL secure server. Which, I suppose that if you just want to use PayPal then you may as well go for that, but if you want a little flexability then this may be a good idea.
Once again I haven’t actually used this, but found a website using it that I had some respect for, so I thought I should keep it in mind cause one day it might come in handy.