Well, please let me know which ones you mean, because all of the following have serious barrel distortion issues at 18mm:

18-55mm, 18-55mm VR, 18-70mm, 18-105mm VR, 18-135mm, 16-85mm VR (the best of a sorry bunch at 18mm), and 18-200mm VR (more expensive, but still has the aforementioned problem in abundance).
I can't seem to find any other Nikon AF-S zooms besides these that can be bought for under about $800, and none of those above pass muster for delivering straight, undistorted lines at 18mm.

The only Nikkors that do are the 12-24, the 18-35 non-AF-s, the 17-35mm f2.8, and the 17-55mm f2.8, and only the non-AF-s 18-35mm is within the budgets of many D40/D60 owners - but, again, with no autofocus on those cameras.

If, on the other hand, you feel that any or all of the lenses I listed in the first group above are perfectly good at 18mm, then we'll simply need to agree that you're a lot less critical about your wide angles than I am. Because they all suffer badly from linear distortion at 18mm. I need a wide angle that renders straight lines as straight, not as arcs.