Ten Five One Grid
Features:
Ten Five One Grid modifies all terrain textures to make it easier to estimate distances in-game by adding thick lines every 10 units, medium lines every 5 units and thin lines every single grid unit. Best used with turning the builtin grid option off (but it can be used alongside it for example if the monitor is not well calibrated and therefore one might have issues seeing the subtle 1:1: grid lines).
Link: Ten Five One Grid