I have the Nikkor 35mm f/2.0D which I love (actually bought it for a D1 at the time). True the downside of it is lack of AF with D40 and D60.
See dpreview.com summary for the AF-S 35mm f/1.8 DX
here. (generally favorable, with one or two weaknesses)
For a collection of links to reviews (for both lenses, and some other 35mm's) click
here.
Again, take dpreview's "cons" list with a grain of salt - for a $200 lens, at this focal length you can't find any better. The only lens IMO that has better optical performance and costs less is Nikon's 50mm f/1.8D, but I don't like the narrow view angle on DX cameras, and, it too won't AF on a D40...
BTW - I was tempted to by the Sigma HSM 30mm f/1.4, I absolutely
hate it: it cost more than $500 and is useless at f/1.4 due to autofocus errors (to add insult to injury, it's also physically large and heavy...)
I ended up ditching the Sigma, and had to stick to the good old Nikkor 35mm f/2.0D - MUCH better, and more convenient to carry.