Besides the obvious beaches ( Topanga, Zuma, Malibu Creek) there is a little town center in the midle of Malibu across from Pepperdine University which is great for people watching, Starbucks, ice cream and lunch.
My favorite place in Malibu is a little restaurant right before Kanon Dr called Paradise Cove. Beautful little restaurant right on the ocean where one can eat and play on the beach. Great for kids, and one might see dolphins which are often seen as you go farther up PCH.
It is quite a trek up PCH from Santa Monica, but if there is no traffic then it is well worth it.