I recently bought the excellent Nikkor 50mm 1.8 lens, a common sight among Nikon photographers of note, and an extremely useful little lens at a great price (just under 20,000 yen). Its advantages are two-fold; you get great up close potrait ability (with out of focus background), as well as useability in low light levels (both thanks to its low 1.8 aperture). Its limitation is the fixed 50mm focal length, a length that is in effect 85mm on the Nikon D40. While this does limit its everyday useability, a fixed focal length without doubt makes you think more about what your photographing, about composing your pictures rather than just being able to lazily zoom in and out from 18-55mm (or indeed 18-200mm in some people’s cases).
30mm would have been better- but the Sigma 30mm 1.4 is slightly out of my (very low) price range.
Heres a shot I took last weekend, of a homeless cat!