1) Take Long Canyon Rd or Main Divide Rd off 74 and go towards Santiago Peak. Easy. Bring mosquito repellant.
2) Powerline Rd from Barstow to Primm, along the north side of I-15. Easy, a handful of small hills.
3) If you don't mind driving out to Death Valley, Titus Canyon, Racetrack Rd, and the trail to Aguereberry Point are all easy and fun. Chloride Cliff is easy to moderate with a small challenge but awesome view at the top.