What's up everyone. I just wanted to make another mention of the increasingly popular Market theme for Wordpress. Market allows you to easily set up your own shop using Wordpress with a pre-made template. You can easily customize the design to meet your specific shop needs. Using tight Paypal integration (and Authorize.net integration coming very soon) you can add items like you would a normal post, set a price, add additional product images, and more - and a buy now button will be generated for you with each post!
If that isn't exactly your cup of tea, there are other ways to use the theme. A plugin is available with purchase that allows you to add a Paypal buy now button to any post with any theme simple by inserting a tag into post or page content. There is also an alternative designed version of the Market theme available in the download center, along with a version which replaces the buy now function with a add to cart function using FatFreeCart (for ajax item adding).
If you are a developer and are looking for an easy way to build a shop for your clients, use the Market theme as a base with a Developer license for just $150!
The market theme is an incredible time saver and has received very few complaints (besides minor issues that were taken care of). All reviews have been very positive and the theme idea is supported by just about everyone. It is also Wordpress 2.5 ready, so no need to worry about incompatibilities!