Thanks Darrel and Marek.
The 10 most popular Pro tutorials have been: Workplanes, Architectural Presentation, Drawing Template, Modern Desk, Modular Cabinets, Radial Engine, Construction Drawings, Gear Pump, Airliner, Face Frame Dresser. Many other have had good sales as well and there have been a couple that have bombed (i.e Window Illustration and Retro Fridge) because of the not so popular subject matter.
Any of the tutorials that give you the best bang for your dollar are the ones that deal with both model and paper space. For instance Construction Drawings, Roll Top Desk and Finger Press Engine. Older ones would include Architectural Presentation and Industrial Shock Absorber.