I ran across this for the first time, and thought it was worth putting together in one spot.  I was trying to deploy a solution into my test environment, which happened to have one web-front-end server offline.  Whether or not that was the cause I have no idea, but the solution decided to sit and wait.  After doing a bit of searching, I came across the canceldeployment command, but either due to bad luck or the net filter at work, I was unable to find out what the deployment id should be.  So I poked around a bit more and finally found the enumdeployments command.

Putting the pieces together you get:

stsadm –o enumdeployments

This will present some XML spew.  It’s easily readable, so find your solution name and get the job id. Then…

stsadm –o canceldeployment –id <id>

This will nuke the pending operation and put your solution into an error state.  You may then retract, delete, and try again.  This same process works for stuck retractions too.