I recently joined Amazon's affiliate program and used their API to create product nodes that contained links to the associated Amazon product. I wrote the code to query Amazon and then create the product node. The theme is just the standard Bartik theme but slightly altered. One module worth mentioning is Google Fonts, which gave me access to some great fonts. The site (http://www.xmasstockingstuffer.com) was relatively simple to build and I had a lot of fun creating it!
I will probably add some cool new features when next Christmas starts to come around :)