anti-static top for a workbench
Any conductive material is fine. In our test lab at work we had the table covered with a 0.5mm aluminium plate.  


  edit following Russell's answer
  DUTs (Device Under Test) in the test lab are mostly packaged end products, so there's no risk of shorting. If a bare board has to be tested an antistatic mat is used, of course.
  For certain tests the device has to be placed at a certain distance above the conductive plate, like when ESD pulses are released to the plate to test the device's susceptibility to induced fields. Here we use non-conductive spacers.


If you want to do it professionally, this picture should give you some ideas:  

  

A wooden benchtop or a stone tile floor don't protect against ESD, but don't induce static electricity either. Cotton clothing also helps.