The current project I'm working on, ProductWidgets, lets you add affiliate products to your website effortlessly. It is backed by the Skimlinks product database that lets you access 25 million products from over 4,000 merchants in 54 countries.
Skimlinks offers powerful APIs to access their huge database of products and merchants. I extracted the code I use to access these APIs to a Ruby gem for everyone to use. You can find the code and installation and usage instructions on Github.