Color
Working with Duotone in Photoshop CS2
Learn to apply duotones to your images using Photoshop CS2.
B&W 2.1: The Channel Mixer
An extension of the tutorial Basic B/W - The Next Step, which teaches you how to achieve great black & white photos using the channel mixer.
Basic B&W - The Next Step
If you want to convert a color photograph to black & white, this is the best method out there.
