I've been working on setting up my new site and decided to try out the WP e-Commerce plugin on it for dealing with selling the products. I would have used Secure Delivery however I need to give the option of a shopping cart to visitors as most will hopefully purchase two products, the main product and an upgrade license (more on this another time).
WP e-Commerce is just like any other plugin for the installation. Just unzip the files and upload the directory to your plugins directory, and activate it in the WordPress admin. You then get an extra menu for it, where you can set your shop settings, other preferences, and start adding categories, brands and product information. It can deal with physical products or digital products, the latter was what I was interested in. You can also easily select which fields to have in the form on the front end, and which of these fields to send PayPal so that they're prefilled. As I'm only looking to sell digital products I took the address details out as these are not needed.
The lite version of this plugin allows you to sell products via PayPal only. Whilst it's called 'lite' it's not that simple as such. You can have your products in categories, there's a shopping basket and it uses the PayPal IPN for instant notification. I've not gone through the whole process but I would assume that if you're selling a digital product it will also then provide a download link to the buyer to download the product, as I've had the option to set how many times the product can be downloaded by the buyer.
There are optional extras that cost a little extra (very little to be honest!) which I may look at in the future if the site gets busy enough to need them. Whilst I could have coded this all myself I figured that it was worth looking at the plugin and to be honest it's a good plugin to use. I may also convert one of our other product selling sites over to it as that's been needing a shopping basket for months but I've just not had the time to sit down and really finish the coding myself. With this plugin I could probably get everything added over a couple of days (100+ products) and convert the site to WordPress and hopefully, if my thinking is right, see the sales rocket
So if you're after a free, light, product selling script then this is a good option to look at.