It has been several years since I took this route, but I would suggest that highway 1 from LA to San Francisco is nice, but until Oregon, it is rather forgettable--perhaps take in Point Reyes and skip the coast until after the Redwoods.
North of LA, take in Santa Barbara--a perennial shooting favorite. Hearst Castle is further North, then the next major point of interest in my opinion, is the area between Monterrey and San Francisco. Wind-swept cypress is the Monterrey Peninsula cliche, there is some fun to be had in the city itself and along the road to Santa Cruz, which has some charm, but not as much as Half Moon Bay, in my opinion (quickly fading due to development, sadly). The stretch between Monterrey and San Francisco is also home to the classic highway 1 fog shot, if you are so inclined and so favored.
San Francisco is of course an excellent subject, as are the Marin Headlands, Muir Woods, and Point Reyes, north of the gate. From there, go up highway 101 until you get to Humbolt. Lisa has already given good information about that. North of Eureka, and especially just after you get into Oregon, the coast really gets nice. There is one beach that I particularly remember, though I have forgotten the name: a state park in the south coast with a light house--otter point? (I know that lighthouses and beaches are hardly uncommon there, but does anyone know which one I am talking about?)
Were the dogwoods in bloom, I would reccommend the road between Crescent City and Salem, but I think in Winter you should stick to the coast and hope for just the right amount of fog.