This is the extruder used on Aluminum Mendel http://www.thingiverse.com/thing:16076. It combines the features of its ancestors that I liked best. It provides more internal filament support than the standard body for less filament buckling. Changeover is very fast.
All items will print without support except the cam. Print body and idler mount in ABS, PLA won't take the heat. I added heat sinks because the X carriage is very narrow in this design without much area to dissipate heat . They are not totally necessary, but do help when using high extruder temperatures.