I'd advise the 18-70mm is the one to go for.. It's fairly cheap and widely available. I bought my D70 with that Kit lens and its very nice; i've had many good and very sharp images using that lens. The only cheaper alternatives would be an 18-55mm or you might find a second-hand 18-135mm. Both of these ar'nt bad either! There is also a newer 18-105mm VR lens which was the D90 kit lens and may be found now. The 18-135mm and the 18-105mm VR have plastic mounts. but the others are metal. (although) not sure about the 18-55mm.
I've now bought the 16-85mm VR; it's very good too, but quite a lot more expensive and mainly lives on my D300 most of the time.