why buy one if you can print one?

for anyone who still doesn´t know this comes very handy:

Free Lens Hoods

Printable PDF documents to make your own lens hoods

This site contains PDF documents that can be printed and cut out to make lens hoods for a variety of 35mm and digital SLR camera lenses. Lens hoods give better quality photographs by reducing flare caused by nonimageforming light.