With the release of KiXtart 2001 there is another solution - KBHit()

This is similar to the original solution, rewritten with KBHit(). If you don't want the count down, leave out the lines marked "; Countdown"
code:
? "Hit any key to cancel: "
$iTimer=15
While KBHit()==0 AND $iTimer
   $iTimer                       ; Countdown
   sleep 1
   If $iTimer > 9 Chr(8) Endif   ; Countdown
   Chr(8) "  " Chr(8) Chr(8)     ; Countdown
   $iTimer=$iTimer-1
Loop
Get $sKeyHit
The $sKeyHit is set to the first key pressed.