Updating database schema with Entity Framework Code First

Entity Framework Code First is a great framework for developing new projects. But what about extending an existing database?

For instance what if I simply want to add an additional property to an existing data entity? Is there any "code first" way to do this or will I have to add a database column by hand using SQL Server Management Studio or a similar tool?

All I have found so far is how to regenerate the entire database from scratch when the schema changes, but I don't want to lose my data.

If I'm not mistaken, there is a tool for Ruby on Rails that can generate an SQL script reflecting the new database changes. Is there any way to do this in EF Code First as well?