The Google Checkout blog announced that they have launched Google Checkout Trends. Google Checkout Trends is a flavor of Google Trends, but limits the data to that collected from Google Checkout merchants.
It basically shows you what people are buying and selling online via Google Checkout. You can plug in one keyword or several keywords separated by comma, and it will show you a chart plotting revenue over time.
At the time I am writing this, Google Checkout Trends is currently not working. I am sure Google is working on fixing it. In the meantime, if you want to see some examples of charts, go over to Google Blogoscoped, which has an example of how many Google Apps were sold over time.
Google has trends for several of their applications, such as Google Trends for the main search index. They also came out with Google Hot Trends in May and Google Reader Personalized Trends about a year ago. Google Finance charts are basically a form of Google Trends, but with stock data. Google News has a form of trends for archive news, as well.