What are some great places to visit on a road trip ...

Well, the road itself is stunning, but you surely know that already. Carmel is a beautiful town, Hearst castle is nice... I can't really remember really

Check out this website.

I agree with Jennie, highway 1 is really beautiful, in Seaside you can stop at "Monterey Bay Chocolates", there are about a dozen state parks along the coast  for picnicing and light hiking . I like the redwood parks just north of Santa Cruz. for ideas of what to do in the cities , you can try these two options,

fun things to do in Los Angeles, California

fun things to do in San Francisco, California

A friend of mine, Richard Rosenblatt, has published a list at that link on city search which details his fav spots for the Los Angeles part of your journey.

For the family: 

Will Rogers State Historic Park

1501 Will Rogers State Park Rd, Pacific Plsds, CA
"Amazing place to let the kids run free--you just can't believe that you are smack in the middle of Los Angeles and not in the middle of Idaho. On the weekends, kids can help wash and pet the horses; it is a lot of fun."

For the Parents:

AIR CONDITIONED
2819 Pico Blvd, Santa Monica, CA
"I am an owner in this bar because I love wine, and we worked hard to create a classy atmosphere, but with a fun element to encourage folks to try different wines. There are no snobs there, just a well-educated team that can guide you on a tour of the senses."