Here in Orange County, CA it has to be Ortega Hwy. (74) running from San Jan Capistrano to Palm Springs. It starts near sea level, crosses two mountain ranges, ends up in the low dessert, and only take two hours. The mountain roads are two lane blacktop with lots of twisties. Its a local favorite for sports cars and motorcycles. I'm sure my neighbors to the north in L.A. will cast their votes for Angeles Crest Hwy.

 

I would have to say crusin the coast around SanDiego is a sweet drive since its all oceanside ect... and Mulhuland

 

In Phoenix, my favorite would have to be the 101 in the afternoon when the sun is setting heading west.