Wandering around a local camping store I came across some floor mats they sell for use in tents. They are made from a closed cell foam, about 500x500mm & about 12mm think and have jigsaw style interlocking edges - they lock together in whatever layout. They also had sloped edge pieces to clip on to stop you tripping over the edges. About $6 each if I remember correctly.

I've had these covering the concrete in front of my table saw & main bench for 6-8 months now - saved me a lot of aching feet, and saved a lot of tools when I've dropped them. Hell of a lot easier to clean up than anything else I can think of too.