Find the largest databases on my server
If you want to query in the INFORMATION_SCHEMA database I have the following:

Total Storage By Database in MB

SELECT DBName,CONCAT(LPAD(FORMAT(SDSize/POWER(1024,pw),3),17,' '),' ',
SUBSTR(' KMGTP',pw+1,1),'B') "DataSize",
CONCAT(LPAD(FORMAT(SXSize/POWER(1024,pw),3),17,' '),' ',
SUBSTR(' KMGTP',pw+1,1),'B') "IndexSize",
CONCAT(LPAD(FORMAT(STSize/POWER(1024,pw),3),17,' '),' ',
SUBSTR(' KMGTP',pw+1,1),'B') "Total Size"
FROM (SELECT IFNULL(DB,'All Databases') DBName,SUM(DSize) SDSize,
SUM(XSize) SXSize,SUM(TSize) STSize
FROM (SELECT table_schema DB,data_length DSize,index_length XSize, 
data_length+index_length TSize FROM information_schema.tables WHERE
table_schema NOT IN ('mysql','information_schema','performance_schema')) AAA
GROUP BY DB WITH ROLLUP) AA,(SELECT 2 pw) BB ORDER BY (SDSize+SXSize);


Total Storage By Storage Engine

SELECT IFNULL(B.engine,'Total') "Storage Engine",
CONCAT(LPAD(REPLACE(FORMAT(B.DSize/POWER(1024,pw),3),',',''),17,' '),' ',
SUBSTR(' KMGTP',pw+1,1),'B') "Data Size",
CONCAT(LPAD(REPLACE(FORMAT(B.ISize/POWER(1024,pw),3),',',''),17,' '),' ',
SUBSTR(' KMGTP',pw+1,1),'B') "Index Size",
CONCAT(LPAD(REPLACE(FORMAT(B.TSize/POWER(1024,pw),3),',',''),17,' '),' ',
SUBSTR(' KMGTP',pw+1,1),'B') "Table Size" FROM
(SELECT engine,SUM(data_length) DSize,SUM(index_length) ISize,
SUM(data_length+index_length) TSize FROM information_schema.tables
WHERE table_schema NOT IN ('mysql','information_schema','performance_schema')
AND engine IS NOT NULL GROUP BY engine WITH ROLLUP) B,(SELECT 2 pw) A ORDER BY TSize;


Total Storage Database and Storage Engine

SELECT IF(ISNULL(B.table_schema)+ISNULL(B.engine)=2,
"Storage for All Databases",IF(ISNULL(B.table_schema)+ISNULL(B.engine)=1,
CONCAT("Storage for ",B.table_schema),
CONCAT(B.engine," Tables for ",B.table_schema))) Statistic,
CONCAT(LPAD(REPLACE(FORMAT(B.DSize/POWER(1024,pw),3),',',''),17,' '),' ',
SUBSTR(' KMGTP',pw+1,1),'B') "DataSize",
CONCAT(LPAD(REPLACE(FORMAT(B.ISize/POWER(1024,pw),3),',',''),17,' '),' ',
SUBSTR(' KMGTP',pw+1,1),'B') "IndexSize",
CONCAT(LPAD(REPLACE(FORMAT(B.TSize/POWER(1024,pw),3),',',''),17,' '),' ',
SUBSTR(' KMGTP',pw+1,1),'B') "Table Size" FROM
(SELECT table_schema,engine,SUM(data_length) DSize,
SUM(index_length) ISize,SUM(data_length+index_length) TSize
FROM information_schema.tables WHERE table_schema NOT IN
('mysql','information_schema','performance_schema') AND
engine IS NOT NULL GROUP BY table_schema,engine WITH ROLLUP) B,
(SELECT 2 pw) A ORDER BY TSize;


Please note in all the queries you see a subquery that looks like this: (SELECT 2 pw)


(SELECT 0 pw) present the Database Sizes in Bytes
(SELECT 1 pw) present the Database Sizes in KiloBytes
(SELECT 2 pw) present the Database Sizes in MegaBytes
(SELECT 3 pw) present the Database Sizes in GigaBytes
(SELECT 4 pw) present the Database Sizes in TeraBytes
(SELECT 5 pw) present the Database Sizes in PetaBytes (If you ever run with this, email me)