The IBuySpy Store application is a great example of how to create an online store using ASP.NET. It's a simple application, yet it does a lot.
The output caching is a great example of squeezing extra performance out of ASP.NET applications. And the use of user controls illustrates how to effectively create reusable components for applications.
You might be interested in locating a white paper that has additional information, at http://www.asp.net/ibuyspy/IBuySpy%20Store%20White paper.doc. A forum on www.asp.net also supports a discussion about the store.