Second the Ivy and Nobu Malibu (and other Malibu places like Moonshadows). Have seen at least one celeb each time I have dined at True Food Kitchen here in Santa Monica. In general any place that has more than your average selection of vegan or raw choices has higher odds of seeing someone you might recognize.

I have a lot of work dinners and every few months have to find a new list to work from -- currently going down the LA ones on this list (not for the celebs, but the food).