In the altnet conference the guys from Microsoft presented an MVC framework that will be released on the spring.
It promise to be something really good, it's seems to be so flexible that you can plug into it whatever framework you are used to. For example, Nunit of MBunit for testing, Spring for DI or NVelocity as your template engine. The framework comes with all this already implemented but they don't force you to use their implementation if you don't want to.
Visit Scot Hanselman's blog for two videos where ScottGu and Hanselman himself demo the framework and right some code. Hanselman does his presentation using IronPython and shows an alternative view engine.
You will need at least two hours of quiet to really enjoy this presentations but they totally deserve it.