I assume the shuttle that exceladdict mentioned is the Ocean Express shuttle.
It runs in a loop from the hotels on Century Blvd to Manhattan Beach, Manhattan Village Shopping Centre, Plaza El Segundo, then back to Century Blvd.
I used it recently while staying at one of the hotels near LAX and had several hours before I had to check in for my flight.
I had enough time for a nice meal at Manhattan Beach, followed by some last minute shopping before heading back to the hotel.
It cost $5 for one loop, and you can hop off and on at each stop if you like.
Just be aware that they don't sell tickets on board, I had to buy the ticket from the hotel concierge.
The shuttle buses themselves are fairly new, but just be prepared for a bumpy ride along Imperial Hwy towards the beach.
The road surface is quite uneven, and the buses could do with some improvements to their suspension...