There are some interesting MSBuild tasks in this project - msbuildtasks.tigris.org.
I'm going to play with FTPUpload and try to add this task to the Continuous Integration server to automatically upload the published package *or* deploy the web site to the test server.
An awesome thing is that automatic FTP can be done conditionally. Check MSBuild Conditions (link) to see how to conditionally execute tasks.
My idea is to run auto-deployment for Test configurations, that would deploy the web application every time it is built and tested, but generate a package for Release builds. The package is to be archived and given to the Ops team for deployment into Production environment.
Edit: Since the solutions for FTP upload above were a bit of a pain to implement, I found another one that works great: http://www.digizzle.com/Projects/FtpTask/Docs.aspx
Edit2: The FTP task above actually works but has a bug in Cleanup command when working with FileZilla server. Fortunately the project is Open Source so I was able to download the code and fix. :)