Here's a recent thread about the very same thing. It's short and offers a few suggestions for different breakers. I think for the most part we are all over the place on what's best for breakers. All are pretty much in agreement on the use of the TVS.
Looking for fuse/breaker suggestions
The TIU has a built in TVS, but installing more here and there like at power connections to the track couldn't hurt a thing and they are very easy and inexpensive. If you select USPS first class shipping, Digi-Key has very reasonable shipping rates and fast too. It is the 1.5KE36CA that seems to be the most popular here.
Digi-Key - Micro Commercial TVS
Digi-Key - Littlefuse TVS
Then there is always the nice shiny new ZW-L that was specifically designed to run our modern electronic trains. I'd love to have one, but those are a bit over my budget for railroad power.