On our road trip last Spring, we stopped at Yosemite for a few days. That's definitely a must-do at one point or another. A little out of the way, so you'd probably want to set aside a full day for that, heading east from Frisco or something early to take in at least some of the sites.
Lunch in the Santa Barbara harbor was pretty nice, too. From there, headed up the 101 to Frisco, another nice drive. You'll pass up the garlic town, too, if you're into that.
Monterey Bay Aquarium was pretty cool. They've got some nice exhibits, San Jose is close and it's a couple of hours south of Frisco.
As was mentioned, San Diego is very nice. Probably about a 2 1/2 drive from L.A. on a nice day. They've got an excellent zoo and wild animal park as well as Sea World. There's also a carrier you can tour, you'll pass, uhh, the San Onofre(?) 'boobs' and will see the sign that warns you for people running across the road. Reminds me of the signs in, I think, Kansas, saying something like 'Hitchhikers may be escapees'.
Around the L.A. area, there's also Knott's Berry Farm, Magic Mountain, Wild Waves(was that the name?). Oh, and also Universal City Walk is pretty cool, too. There's also the Walk of Fame and Hollywood Blvd.
If you want to get your oohs and aahs on, you can check out the Beverly Hills area or you can go up to Palos Verdes and get a nice view, too. Pacific Palisades is nice and has a view, but many of the nice places are behind walls from what I remember. Up in Palos Verdes, they've got a few look-out spots as well that allow you to see just about the entire city area.. ah, and they've got some nice cliffs above the ocean, some of which are slowly falling into the sea.
Another day trip could be to Catalina Island.
If Venice may be a bit busy for your tastes and you just want to experience some nice beaches, you could stop by Hermosa Beach, which is still 'hip' and kind of busy, but not as packed as Venice.
Tons of stuff to do in Frisco, too. Even with a week or two, you still couldn't manage to do a fraction of the things in either city.
Oh, the Golden Gate Park and the Presidio were pretty cool, too.