CruiseControlLevels adds three speed levels to the cruise control. Basically, this script is like SpeedControl by Heady. But unlike SpeedControl, CruiseControlLevels keeps the default cruise control keys (1,2,3) with their default function (increase/decrease speed, activate cruise control). Switching speed levels is possible with lshift+4 (1->2->3) or lctrl+4 (3->2->1). Default speeds for these levels are 10, 20 and max speed.
Just put the zip file in your mods folder. Download it here.