I mentioned the Spark View Engine that I demonstrated at the Tampa MVC Firestarter Event and am using for development with the ASP.NET MVC Framework.
In addition to my sample, Phil Haack has also put together a sample of using the Spark View Engine using Northwind here.
As Phil mentions, the Spark View Engine is also available for Castle MonoRail, IronPython, and IronRuby, so it is just not limited for use with the MVC Framework.
By all means you do not have to use any other view engine other than the webforms view engine. It is nice to have options, however, just as we have options of VB.NET, C#, F#, IronPython, IronRuby, etc. to develop .NET applications.
You can learn more about the Spark View Engine here.