My opinion is that the D40 is the best in terms of value for money...it has better noise control, it is cheaper and has faster flash sync speeds.
The d40x just has a higher megapixel, higher noise, higher price, slower flash sync. The d60 has a sensor cleaning tech but has mixed results..an air blower will probably be much more effective, besides i use a D80 and change lens very regularly with not much issues with dust. The d60 still has higher noise and slower flash sync speed. The only major point i feel is the inclusion of a digital range finder which is better for manual focusing than the "green dot" on the d40. A split focusing screen on the d40 will give you a better manual experience anyway, than the digital rangefinder.
Another minor advantage is smaller file sizes on the 6 megapixel, where you wont need a large memory card. And a 6 megapixel raw file loads significantly faster than a 10megapixel.
I feel that TS should just get the cheapest D40 he/she can find, learn then move up to a d80/d90/dxxx which is probably a better step up.