A couple of materials (PLA and ABS) have been historically used by the 3D printing enthusiasts (Reprap community) on desktop fused filament deposition 3D printers. Polylactic acid (PLA) is a renewable plastic, while acrylonitrile butadiene styrene (ABS) is a widely used engineering thermoplastic. Thus 3D printed objects could be made having different physical properties, in both renewable and engineering grade plastics.  

As the desktop 3D printing community evolved, it became clear that in order to take advantage fully of the additive manufacturing technique, for example to build fully functional parts, there was a need for accessing a more diverse range of physical properties. As such a larger number of 3D printed materials was needed. The vast majority of the hobby and desktop 3D printers are based on the fused filament deposition (FFD) technique which uses thermoplastic materials, so accessing more of the industrially used engineering plastics seemed a natural development. 

Another reason for a larger number of 3D printer materials came from the fact that single extruder machines, while exceedingly good at printing solid or mostly vertical walls, are not very good at printing overhangs or steep sided walls. Simply put, you can't print a layer of new material in air. So it became obvious that a dual extruder machine in conjunction with easily removable material was needed. Yes, you could use a single extruder machine to print support structures of the same material as the wanted 3D part, but then, some times extensive, post processing is needed in order to clean the support structures. The easiest way would be to use a second extruder to print a dissimilar thermoplastic which then could be removed by dissolving it in some solvent that does not affect the thermoplastic used to print the main part. 

Moreover, a combination of thermoplastic materials with different properties (hardness, elasticity, color...) within one 3D printing object is some times desired or fun to have it, which can be achieved easily with dual extruder machines.

This is a fast evolving scene with more and more thermoplastics being tested. The following is a collection of printing recipes based on my 3D printing experiments with these materials. All the materials were printed with at least one of the ShapingBits 3D printer models so, temperature readings reported for extruder and heated bed could be slightly different for a different 3D printing bot. Since each material has its own strengths and difficulties within this technology I start with a summary list form of all the materials I've tested. For more details of the 3D printing process, please follow the links in the names.