Missing in the NEX lens line-up is a "fast standard" type lens. I have two lenses that, via manual focus might fit the bill. The first is a Voigtlander 28mm f/2 Ultron which I liked very much when I tested it here: http://soundimageplus.blogspot.com/2011/10/sony-nex-5n-and-manual-focus.html
The second is the last piece of Nikon kit that I still have, and deliberately kept to see how it works with the NEX-5n.
Sony NEX-5n Nikon 35mm f/1.8G
I went out yesterday, when it stopped raining, to try it out.
The results were very good, its a sharp lens, even at f/1.8. There is some CA and purple fringing wide open. Operationally its more difficult to use than the Voigtlander. I have an adapter that lets me change the aperture, but its very difficult to guage what I'm using as there are no markings. f/1.8 is easy enough but the rest is guesswork and can only be estimated by looking at the shutter speeds. Most of the above were taken (probably!) somewhere between f/5.6 and f/11. I really can't be more specific than that.
This morning however, a more satisfactory solution appeared. The LA-EA2 adapter has become available and I have ordered one. This should allow me full-speed AF on a-mount lenses, though with the loss of 1/3 to 1/2 a stop. I'll test it out and see how that works. The a-mount 35mm f/1.8 would then give me the light gathering abilities of an f/2 or f/2.2 approx. Is that enough when combined with the 5n's high ISO abilities? I'm not sure but I'll find out soon.