Like most parents I spent too much money, yet I knew in advance what my kids' favorite presents would be: Laser pointers from the dollar store. My son hasn't even touched the Hot Wheels crap, but he and his sister have been teasing the dogs for hours with these stupid lasers.
Progress is amazing. As a child in 1979 I'd never, ever imagine that in 30 years I'd be able to buy laser devices for my kids for a buck each.
Their favorite toys, in order:
1) Cheap laser pointers
2) Nerf guns
3) "Daddy, did you get any new games on your iPhone?"