synclient touchpadoff=1 to disable touchpad and
synclient touchpadoff=0 to enable touchpad.
$synclient | grep TouchpadOff TouchpadOff = 1
I'd like to create script that will toggle this value. Then I will bind to key in OpenBox.
Note that there is a third setting, "TouchpadOff = 2", where only tapping is disabled.
Another possibility, a oneliner, but not a very efficient one: