If you're using Visual Studio, the answer is SQL Server Data Tools (SSDT). It comes with SQL Schema Compare functionality. Check it out here: http://msdn.microsoft.com/en-us/data/tools.aspx
SSDT can also do a lot of other stuff, like automated database testing, automated build and deployment of databases, etc.
There are also 3rd party alternatives, such as Red Gate's SQL Compare: http://www.red-gate.com/products/sql-development/sql-compare/