I use a rubber car mat I bought from tesco (their "value" range") for about £2, originally I was after a £1.99 rubber door mat from Wilkos but they were sold out.
It worked a treat !!
Was running a fully speced PC complete with HDD & DVD, and installed the o/s and burnt in to ensure all was OK.
Also to switch it on I just shorted the 2 pins for the power switch with a screw driver.
Diddy