Pickup/Dropoff: Tour providers usually pick up and drop off outside the terminals at LAX. Details will be provided by the tour company.
Luggage: You can (usually) bring your luggage with you on the tour van, if needed. Be sure to confirm with the tour provider if you need this option.
Time estimate: Suitable for a layover of around 6 hours or longer. Your flight needs to arrive about an hour before the tour time, and depart an hour after the tour dropoff. International flights will require additional time to go through customs.
[May 2021 update - these companies are open]
Freedom Tours L.A. - Private tours for 1 to 6 passengers, providing tours starting from 4 hours. This is a good option for small groups.
ToursByLocals Private Los Angeles Layover Tour - Customized private tour that can be personally arranged to pick you up from the airport on your Los Angeles layover, see the places that most interest you around, and then return you to the airport.
Real Los Angeles Walking Tours - Private 2-hour walking tours of downtown L.A. or Hollywood.
[May 2021 update - this tour relies on the LAX FlyAway Bus, which currently does not provide service to Hollywood]
Glitterati Tours from LAX Airport - Customized city tour. You can get dropped off at your hotel instead of returning to the airport.
American Riviera Tours LAX / Long Beach - Provides layover tours from LAX airport and from cruise terminals in Long Beach and San Pedro.