I was always taught to show my appreciation with two simple words as a minimum of gratitude to not only the bus driver but the bus service as well. When you consider the money you are saving in gas, the small carbon footprint you are leaving and the ability to leave your care in the garage, riding the bus is quite a benefit. A simple "thank you" is the least you can offer.
In the city where I live, it is amazing to watch how many people thank the bus driver upon their exit and quite encouraging. It really does help start the day off with a positive step in the right direction and carrys through with everyone I come in contact with throughout the day. Try it.
Today, as I exited the bus, I thanked Lloyd for a smooth ride and it seemed to perk him up a bit. Evidently he was making a special effort to make the ride a more enjoyable experience for everyone and my thanking him let him know how it set him apart from the rest of the bus rides I had been on. He was doing an exceptional job and appreciated being recognized for it. It didn't cost me anything but I bet he'll remember me the next time in a positive way.