Brio is a swedish railroad toy. It is hideously expensive, although extremely fun. Tracks are made of non-splintering wood that comes in numerous shapes. As well as curves and straight pieces, there's also bridges, ramps so you can custom build your bridges, connecting pieces so that the trains can go either way, turn-wheels, bridges that lift up, and tons of other stuff
It's very fun for 2-7 year olds just to watch the trains go around, but at around 10 you start to appreciate the engineering (well, if you're a geek, anyways).If you have quite a lot, then you can make fantastic tracks with numerous bridges and cross-sections.
Recently, Brio has come out with electric train engines, which are very cool, though very expensive.
Brio is very nice for people who like the idea of trains, and would get into model railroads, if they had the time/money/whatever.
A final benifit is the fact that all Brio pieces are guarrantied for life. If you take them to any good Brio-selling store, they will be replaced, even if you don't have a receipt.