That having been settled by necessity, there were wood, plastic, and soft. In various colors. Nothing else had changed since my father's outdoor privy.
What boring lives we led! Now you have a choice of round or oblong, of course. There are toilet seats that close noiselessly. Toilet seats that remove from their hinges for cleaning; others that contain a potty option in case you are toilet training a toddler. Seats that light up at night (Batteries not included.). All sorts of plastic, with designs or flowers or seahorses embedded. Wooden seats with veneers to match your dining room table. And of course, customized seats such as the one pictured above and others that cannot be described in polite company.
For less than $600 you can buy a heated toilet seat which washes the relevant body parts and even blow dries them. Of course, you need the services of a plumber and electrician if you want them to work..