Source:
The RAW samples are downloaded from Imaging Resource's Still Life test

Lenses and files used:
D90: Nikon AF 105mm f2.8D micro, @f8 12bit NEF
D300: Sigma AF 70mm f2.8 EX DG macro, @f8 14bit NEF
50D: Sigma AF 70mm f2.8 EX DG macro, @f8 14bit CR2
40D: Canon EF 100mm f2.8 macro, @f8 14bit CR2

RAW conversion:
I used RawTherapee v2.4beta1 (dcraw 8.88 build), EAHD demosaicing algorithm processed to 16bit sRGB TIF,
neutral profile, no contrast NR and sharpening, In-camera WB (custom made by IR), Exposure compensation between +1.10 to +1.30EV with all cameras to give color checker's white patch a RGB value of 220. Presentation made in Photoshop CS3 with no processing except 100% cropping and conversion to 8bit JPEG for web presentation.

I added Photoshop pixel statistics standard deviation values (red numbers) for the color checker's black patch to give some impression of the noise levels.