Planking

I came across Hardi-Plank and Hardi-Panel several shows back when a fellow TD student used it in a production he was doing.

The material is a fiber compost - cement material. You do need special saw blades, as they dull regular blades very quickly. The plank is used for siding and the panel is used for flooring. It is good for waterproofing, and fireproofing. It paints well (it requires paint for finishing) and is very durable. It is less expensive than lumber and come in several different textures so it can simulate real planks.

In use it was found to be better than comparable OSB or hardboard products.

For more information:
http://www.jameshardie.com/
http://www.jameshardie.com/homeowner/prodcomp/default.php

Another product that was discussed was boxcar siding. Its basing stick lumber with tongue and grooves meant to be joined together for siding, often used in the older box cars. There are many types available (lumber, widths, ect).
For more information:
http://www.wrcla.org/cedar_products/cedar_siding/tongue_groove/default.htm
http://www.thepellco.com/Moldings/Tongue/TongueGroove.htm

Also, I should note that some of these materials are used for wainscoting.