A cautionary example: Patterson originally wrote NYPD Red as a stand-alone about a special task force for celebrity crimes. It sold so well he turned it into a series (currently 7 books). So even Patterson doesn’t always know which stand-alones will stay stand-alones.
In addition to the novels mentioned above, James Patterson has written many other notable stand-alone novels, including: james patterson stand alone
While this features his famous detective Alex Cross, it is often cited as his best work. It is darker, tighter, and scarier than almost anything else he has written. It is the gold standard of his style. A cautionary example: Patterson originally wrote NYPD Red