[codesyntax lang="sql"]

SELECT CONCAT(table_schema, '.', table_name),
       CONCAT(ROUND(table_rows / 1000000, 2), 'M') rows,
       CONCAT(ROUND(data_length / ( 1024 * 1024 * 1024 ), 2), 'G') DATA,
       CONCAT(ROUND(index_length / ( 1024 * 1024 * 1024 ), 2), 'G') idx,
       CONCAT(ROUND(( data_length + index_length ) / ( 1024 * 1024 * 1024 ), 2), 'G') total_size,
       ROUND(index_length / data_length, 2) idxfrac
FROM information_schema.TABLES
ORDER BY data_length + index_length DESC
LIMIT 10;

[/codesyntax]

Source: http://www.mysqlperformanceblog.com/2008/02/04/finding-out-largest-tables-on-mysql-server/