I wanted to update the answers here as I recently talked to a seller who had personalized plates which he had taken off the car, claiming that it was legal for me, the buyer, to drive a car with no plates, just tape the registration to windshield. That was completely not true. It is the sellers responsibility to get no fee regular license plates. From the Ca DMV website:

“What do I do with the license plates when I sell my car?
 Most vehicles have sequentially issued "standard" license plates that remain with the vehicle when ownership is transferred. If the vehicle has a special interest or personalized license plate, these plates belong to the plate owner, not the vehicle. Aas the seller you must decide if you want to retain the license plate for use on another vehicle, or release your interest in the license plate. You (meaning the seller) may remove the plates for reassignment to another vehicle or retain for future use and apply for a no-fee Regular Series License Plate. This should be done prior to obtaining the smog certification (if required). Depending on the type of license plate, complete a Special Interest License Plate Application (REG 17) form or a Special License Plate Application (REG 17A) form to indicate retention or release of the special license plate and give the form to the buyer. If you are releasing the plate ownership to the buyer, the buyer would also complete a separate REG 17 form.”

Link to Ca DMV page about changing vehicle ownership, above about half way down page in FAQ’s. HTVR 32