Ever since I used a stock trading application written in java applet available at tdameritrade.com (initially offered by Datek), I have become interested to find a similar stock trading application in .NET that runs as well or better. While it is just a sample application, StockTrader caught my interest. It is a service-oriented enterprise application developed with Windows Communication Foundation (WCF) and ASP.NET, and designed as a benchmark kit to IBM WebSphere's Trade 6.1 sample application. According to an eWeek article, the .Net solution has demonstrated significant performance advantage. You can find more information on the application and download source code at the StockTrader site.
If you are interested to see how four .NET 3.0 components work together, review the sample application of http://www.dinnernow.net. The demo utilizes several technologies including Windows Communication Foundation, Windows Workflow Foundation, Windows Presentation Foundation, Windows Powershell, ASP.NET Ajax Extensions, Linq, the .NET Compact Framework and IIS 7.0.