Where to go in California, Hollywood or Santa Monica... or somewhere else? Please help.?

I am travelling the USA in April / May 2010. The final part of my journey is the West Coast. I’ve already booked 4 days in Vegas and 4 days in San Fran. I then fly into LAX on May 20th for 3 days before returning to the UK. I am finding it very tough to decide where to go. I originally planned on going to Hollywood but I have since heard it is not a nice place and there is not that much to see. I won't have a car and LA looks very spread out so I am now swaying to going to Santa Monica and chilling out on the beach for three days. My problem now is will it be warm enough at the beach from May 20-23? What do you suggest or are there any other places I should stay go?