This site was recommended to me by one of the staff at PermaJet. Northlight Images Photography Tutorials and How-to articles are well worth reading
More than that though
Not everyone wants to/ is able to afford one of those Spyder things for calibrating the screen. They are expensive and the process is a bit of a fiddle. Yet they fulfil a certain need, ensuring that what you see on the screen is similar to what comes out of your printer. In short if the screen isn’t calibrated correctly then how dark or light your prints will be becomes something of a guessing game. Wasted paper, wasted ink and all that! Worse still if images are being sent away to a commercial printer it seems doubly important to have correct colours on the screen.
Northlight images have both colour and black and white test sheets which can be downloaded free of charge and sent through your printer. These graded B&W and coloured images show at once where problems might be.
Instant diagnosis Printer Test Images