for stamping you might want to avoid harder metals as they cause tool wear, if you are dead set on something durable/hard wearing and can cut, i would suggest case hardening after (although work hardening around the edges of teh stamped part are pretty much there). Have a look at CES (Cambridge Engineering materials Selector) and find a decent high carbon steel (if suitable) or a tungsten coated/tipped edge, depending on situation etc.. the answer for your question depends on budget, situation, context, environmental settings, engineering challenge (I.E. Direction of stresses involved) and you should be solving them through teh application of science, common sense and penny pinching. Welcome to the world of making things.
Seems like the OP isn't clear on what they want in terms of properties. i agree with kingred, but i guess thats because are backgrounds are identical. But to humour the thread, the hardest metal i could find is Osmium, found via my personal library of information, but easier to show via wiki. If its for stamping then tool steel like AISI S1 would be suitable.
The hardest naturally ocurring metal would be Iridium, or Osmium, however I believe Iridium steals the crown (if memory serves me). As for alloys I'm not sure, but possibly tungsten carbide as others have suggested.
Just looking up on my periodic table, looks like Cesium? I believe the bottom left corner gets more reactive and also softer, though I'm not sure if Francium would then be even softer...
