Rob Fox has blogged today about how he resolved a problem where the MSMQ snap-in missing in MMC console. He found that re-registering the MQSNAP.DLL file did the trick.

I've had a look at the support case archive and you may need to re-register ATL.DLL too first. It all depends on what the root cause is and tools like Process Monitor should help to isolate it.

Note - don't get caught out by a stopped MSMQ service; this state will ensure "Message Queuing" doesn't appear under "Services and Applications" in the same way.