When I was young, I loved train rides. I didn't have much opportunity to sit on trains then. It's not like now with commuter trains and light rail transport (LRT). People who live in places where riding the subway is a way of life probably thinks I'm crazy to desire to sit on a train. But living in Malaysia before the 90s, if you sat on a train, it was to go on a long trip north/south. For me, that usually meant rare holiday trips.
However much I liked to sit on trains, I never did play with train sets. My kids haven't asked for them either. I know my son is more into dinosaur and dragons then into trains and cars. But I do know of many other kids (friend's children) who are obssessed with trains as my son is with his dinosaurs.
Usually when you talk about train with kids, Thomas the Tank Engine is mentioned. Well, if you are a train collector, or is raising one, Shopping.com has a good collection of trains for you. They have 962 different kinds of trains cars and train sets for you to choose from. Caboose, stock cars, steam engines, diesel engines, tanks, box car, food service car... you name it, they got it. You also have 27 different brands to choose from. Thomas and Friends, Learning Curve Toys, Seth Thomas, are more suitable for young children.
Not into trains but into fast cars and heavy duty machines? Just check out their "vehicles and raceway" category. Not only cars and excavators, but also available are planes/helicopters and spaceships.
For each item, they have price comparisons from various shops. You can also read shop reviews to check out customer service and customer satisfaction. This way you can decide if you can trust the seller or not.