I created a industrial design sketch rendering tutorial a while ago.
Basically it is showing what tools and techniques I use to render a quick concept sketch line drawing using the mouse only. No pen tablet is needed, really.
The time I spent for this one is around 1 hour, including making the screenshots.
In my daily work, I think I must be able to render 8 of these illustrations in one day. They can be used for internal concepts reviews, or even reviewing with the client in the early concept stage.
Of course you can spend more time on more details, but for this demo the purpose is to quickly render the basic coloring,shading,lighting and highlights.
Check it out HERE