This one may be obvious to some and not too old, but here it is:
Got a socket-head cap screw with a rounded socket from a cheap hex key set? How do you remove it? Take your trusty die-grinder (Dremel Moto Tool), and with a cut-off wheel, carefully slice a slot into the screw head and remove with a flat blade, appropriately sized screw driver.
If it is too tight, chuck the screw driver blade in your drill press and turn the chuck by hand. This allows you to maintain exact downward pressure on the screw head and not let the blade slip and round out the slot!
