I think for California it might be shorter to list the roads that *aren't* fun.
The obvious ones in NorCal are:
* The Hwy 36/3/299 loop up near Redding/Fortuna
* Lost Coast
* Anything in Gold Country or the Sierras
* Santa Cruz Mountains in the Bay Area
* Hwy 1 pretty much from Oregon all the way down to SoCal