The sys.dm_os_waiting_tasks DMV contains a wealth of useful information about tasks waiting on a resource, but until now detailed information about the resource being consumed - sys.dm_os_waiting_tasks.resource_description - hasn't been documented, apart from a rather self-evident "Description of the resource that is being consumed."

Thanks to a recent Connect suggestion this column will get more information added. Here is a summary of the possible values that can appear in this column - Note this information is current for SQL Server 2008 R2 and Denali:

Thread-pool resource owner:
•       threadpool id=scheduler<hex-address>

Parallel query resource owner:
•       exchangeEvent id={Port|Pipe}<hex-address> WaitType=<exchange-wait-type> nodeId=<exchange-node-id>

Exchange-wait-type can be one of the following.
•       e_waitNone
•       e_waitPipeNewRow
•       e_waitPipeGetRow
•       e_waitSynchronizeConsumerOpen
•       e_waitPortOpen
•       e_waitPortClose
•       e_waitRange

Lock resource owner:
<type-specific-description> id=lock<lock-hex-address> mode=<mode> associatedObjectId=<associated-obj-id>
              
<type-specific-description> can be:
• For DATABASE: databaselock subresource=<databaselock-subresource> dbid=<db-id>
• For FILE: filelock fileid=<file-id> subresource=<filelock-subresource> dbid=<db-id>
• For OBJECT: objectlock lockPartition=<lock-partition-id> objid=<obj-id> subresource=<objectlock-subresource> dbid=<db-id>
• For PAGE: pagelock fileid=<file-id> pageid=<page-id> dbid=<db-id> subresource=<pagelock-subresource>
• For Key: keylock  hobtid=<hobt-id> dbid=<db-id>
• For EXTENT: extentlock fileid=<file-id> pageid=<page-id> dbid=<db-id>
• For RID: ridlock fileid=<file-id> pageid=<page-id> dbid=<db-id>
• For APPLICATION: applicationlock hash=<hash> databasePrincipalId=<role-id> dbid=<db-id>
• For METADATA: metadatalock subresource=<metadata-subresource> classid=<metadatalock-description> dbid=<db-id>
• For HOBT: hobtlock hobtid=<hobt-id> subresource=<hobt-subresource> dbid=<db-id>
• For ALLOCATION_UNIT: allocunitlock hobtid=<hobt-id> subresource=<alloc-unit-subresource> dbid=<db-id>

<mode> can be:
• Sch-S
• Sch-M
• S
• U
• X
• IS
• IU
• IX
• SIU
• SIX
• UIX
• BU
• RangeS-S
• RangeS-U
• RangeI-N
• RangeI-S
• RangeI-U
• RangeI-X
• RangeX-S
• RangeX-U
• RangeX-X

External resource owner:
•       External ExternalResource=<wait-type>

Generic resource owner:
•       TransactionMutex TransactionInfo Workspace=<workspace-id>
•       Mutex
•       CLRTaskJoin
•       CLRMonitorEvent
•       CLRRWLockEvent
•       resourceWait

Latch resource owner:
•       <db-id>:<file-id>:<page-in-file>
•       <GUID>
•       <latch-class> (<latch-address>)

Further Information

Slava Oks's weblog: sys.dm_os_waiting_tasks.
Informit.com: Identifying Blocking Using sys.dm_os_waiting_tasks - Ken Henderson

- Guy