AC/DC motor stall protection after the fact
For the DC motors a PTC resettable fuse can be put in series with the motor.  You'll have to find one that has hold current high enough to run the motor as normal, but trip current low enough to stop the current if it stalls AND also have maximum voltage greater to the maximum applied motor voltage.  An example of a PTC is here:  http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&amp;name=F2152TR-ND

Digikey has lots of PTCs available. Take a look.