A lot of the agents here have already mentioned San Pedro. You may consider Long Beach as well.
Here's a link to a blog that I recently posted about these areas.
Port Hueneme and the Oxnard Harbor area are also promising investments. As the coastal farmland in Oxnard is developed over the next 20 years, these areas will become high demand beach property.
You may also take a look at San Clemente and Oceanside where interesting deals still occasionally come up, as compared to the surrounding communities like Laguna & Carlsbad.
Finally, you can still get beach community homes in L.A. for $550k-$700k in Redondo Beach, El Segundo, Westchester & Venice. Not cheap... but considering the alternatives. I have a permanant search set up for the 100 least expensive homes from El Segundo to Redondo Beach on my website. The link is at the bottom of this comment.
Please feel free to contact me if you have any questions or would like more information about some of these options. Here's one more link to a great free tool called Market Snapshot that may be useful to you. It will give you this week's housing conditions including community reports for any neighborhood from L.A. & Orange County to San Bernardino.
Best of luck.