Catalina Island is nice - most folks usually plan on taking the ferry over and spending the night. It can be done as a day trip, but it makes a much nicer overnight.
The reason I asked what you were into is because I had some off the beaten path tourist ideas. If you are into hiking, picking up a lunch at a lobster shack on the PCH and hiking up into Topanga National Park is a lot of fun. Great views of the ocean and the Valley at the same time! Also, another great outdoor experience in the Paramount Ranch - reached from the 101.
Quirky local things up in Los Feliz included a special appointment to see the Ackerman Sci Fi museum - in Mr. Ackerman's home!
I'll just start there. Let me know if you want more!!!