I'm pretty sure it's...
Entry-level: D50, D40, D40x
Mid-level: D70, D70s, D80
The D40 had improvements over the D50, like a bigger, better LCD, but it took away the top LCD and especially the focus motor. I think that if it weren't for the focus motor, the D40 would be much more loved than it is. That's certainly the only thing that holds me back from an unqualified recommendation it to people.