Phil Haack just posted about REST and ASP.NET MVC.
He explains why the WCF team at Microsoft has put together an SDK and samples for building REST services using ASP.NET MVC.

The post can be found at: http://haacked.com/archive/2009/08/17/rest-for-mvc.aspx

I'll be giving this SDK a go, and keep you updated on my findings.

You might also want to take a look at this article about building a WCF REST client: http://damianm.com/tech/building-a-rest-client-with-wcf/