mySQL: size of the database

SELECT table_schema "Database",
SUM( data_length + index_length ) / 1024 / 1024 "Size (MB)",
SUM( data_free )/ 1024 / 1024 "Free (MB)"
FROM information_schema.tables
GROUP BY table_schema ;

This will work in mySQL 5.0.2 and newer. Use SHOW TABLE STATUS command for other versions.