I created a set of gradients in Elements to mimic some of the classic duotones of black & white photography. I used a Gradient Map adjustment layer and Multiply blending mode to apply them to an RGB black & white image. Very subtle.

This set of gradients is available at Adobe Studio Exchange: http://www.adobe.com/cfusion/exchange/index.cfm?event=extensionDetail&extid=1043526
If the link doesn't work for you, search Photoshop type files for Classic Duotones or by item# 1043526.