SQL Server 2008: How to query all databases sizes?

Question

I have MS SQL 2008 R2, 500 databases. What is the most efficient, easiest and \'modern\' way to query all databases sizes.

The output should have columns:

Answer 1

Simplified & Improved version:

SELECT
    D.name,
    CAST(SUM(F.size) AS bigint) * 8*1024 AS SizeInBytes,
    CAST(SUM(F.size*8.0)/1024/1024 AS decimal(18,3)) AS SizeInGB
FROM 
    sys.master_files F
    INNER JOIN sys.databases D ON D.database_id = F.database_id
GROUP BY D.name
ORDER BY SizeInBytes desc