Seeing that the Nikon D40 will not be able to autofocus with famous lenses such as the $100 Nikkor 50mm f/1.8D AF, D40 owners desiring short prime lenses will have to turn their attention to the one lens from Sigma that seems to fill the need nicely.
Collected here are links to related reviews, user impressions and sample images from the Nikon D40 plus Sigma 30mm f/1.4 EX DC HSM combination.
Sigma 30mm f/1.4 impressions and images by Deanx0r
Dean shares four sample images (resized without any other postprocessing) shot with the Nikon D40 + Sigma 30mm f/1.4 and comments that the Sigma is a delight to use in lowlight situations, autofocusing nicely on the D40 and produces sharp photos. Read his remarks and view a larger version of the pics here.
Review and Impressions by AndreasE
AndreasE has some interesting comments to make about the Sigma here and shares some pictures of the Sigma mounted on the D40 here.
Sigma 30mm vs Nikkor 35mm f/2
Vince mentions that the Sigma 30mm cannot be beat for value, and produces extremely sharp photos when stopped down to f/2 to match the Nikkor 35mm f/2D AF lens. F/1.4 is truly handy in lowlight situations where flash is not allowed.