Get blocking information

SELECT t1.resource_type,

        t1.resource_database_id,

        t1.resource_associated_entity_id,

        t1.request_mode,

        t1.request_session_id,

        t2.blocking_session_id

FROM sys.dm_tran_locks as t1

INNER JOIN sys.dm_os_waiting_tasks as t2 

ON t1.lock_owner_address = t2.resource_address

http://msdn.microsoft.com/en-us/library/ms190345.aspx