Besides the default reports, I have one custom report I've created. It is called the "Alerts - Failed Windows Logons".
Table: Windows Accounting
Fields: Count(MessageID), MessageID, UserName
Sort Order: count(MessageID) (Descending)
SQL where clause: EventLog = 'Security' AND Reason NOT IN ('An unexpected error occurred during logon') AND (MessageID IN ('Security_675_Security') OR MessageID IN ('Security_672_Security') OR MessageID IN ('Security_676_Security'))
Please post your custom reports with specifics.