I am a big fan of SubSonic being a .NET developer and Ruby on Rails evangelist.
Developing ASP.NET applications in SubSonic is a much more productive task as it takes all the benefits of Rails into the .NET environment. Subsonic is a zero code DAL (Data Access Layer) providing rich data features.
The one thing i love about this tool is being able to get a site up and running quickly using the scaffold. I just use the scaffold function as a temporary development environment until I am ready to build the templates ans start implementing some CSS to get the UI designed.
The new command line tool is a great addtion to SubSonic and provides a lot of cool generate functions and much more.
Check out SubSonic at http://www.codeplex.com/actionpack