Currently I m working on shopping cart application . I found some cool and very helpful articles where guys describe the way in which they write shopping cart application in dot net. These are the best links which I found on net.
Building an ASP.NET Shopping Cart Using DataTables I found this cool article on site point.
From Code project
http://www.codeproject.com/aspnet/shopcart.asp
http://www.codeproject.com/aspnet/ShoppingCartCSharp.asp
best article if u good in object oriented programming this article is really good by david.hayden on codebetter web site http://codebetter.com/blogs/david.hayden/archive/2005/03/22/60166.aspx