I like to ride Old Topanga > Mulholland Hwy West > Little Sycamore Cyn Rd > Yerba Buena Rd. > Cotharin Rd. > Pacific View Rd., which leads to Deer Creeek Road, the CRAZIEST descent in the Santa Monicas. And great views, if you dare look.
This route through the mountains gets you a lotta elevation gain, as the mountains are never level. Lotta nice views. But Deer Creek is the cherry on top.