I have to admit, I never end up using Blender at all. But sometimes I come across a tutorial that shows how impressive Blender is for free open source 3D software. This is a tutorial shows a script that allows sketching meshes using the grease pencil. It can be used to sketch meshes from the ground up or also for doing retopo.
Surface Sketching for Blender (tutorial version) from Blend_Ideas on Vimeo.
