Removing a stripped(ish) hex c'sunk bolt

[robinbanks]

Angle grinder with a cutting disc in; make a cut right through the blade and the bolt head, down to (but not cut into) the metal into which the bolt is screwed. The blade comes off in 2 pieces, releasing its grip the bolt head,, and then you have a nice slot in the bolt head to turn with a screwdriver.. If the bolt head drops to bits, turn the remaining stub with pliers

 

[Old Salt]

Try all the options that have been suggested without destroying the screw. If none of those work then you can resort to centre punches and hammers, etc.