如何处理网站数据库的进化设计?

I am about to start my first project on an ASP.NET MVC 3 web-site. This site will have data storage and I am wondering what's the best way to deal with the evolutionary design of the database behind the web-site - after the site launches, it will be extended and it will keep on growning thus database refactoring will be an issue. What's the best way to deal with this "problem"? I was thinking of using an ORM like NHibernate or Entity Framework, but neither of them support evolutionary database design.I am about to start my first project on an ASP.