Blender Video Tutorial - Scratch Modeling
This first video discusses a quick and dirty method for making scratch models. I would recommend starting with the second video if you are just learning about scratch modeling.
Shutter's method for scratch modeling is one of the best I've seen for inserting reference. I've tweaked his method just a little to aid in keeping things fairly straightforward and as repeatable as possible.
This video covers how to make a propeller.
Recycling animations can be an easy way to push your limits.
Making a 5-point star can be a bit difficult if you don't know this handy trick!
Smoothing out a mesh is an important process for every addon to look well.
Using the Subsurf Modifier
Making a flat-facing canopy is something that can be difficult to make.
Making an engine Nacelle from scratch.
Making a fowler flap.