One of my favourite pens, if not the favourite is a brush pen by Pentel. It is an inexpensive yet good quality synthetic filament brush pen that uses cartridge ink. It’s great for drawing and calligraphy as it can produce a wide variety of line widths. It is available in black, brown and grey - ink and body. 

The brush pen proves particularly useful when doodling small figure drawings in silhouette. Because quite heavy line widths can be produced through applying extra pressure to the brush nib it doesn’t take long to give the suggestion of form. Below is an image of the brush pen compared to a standard nylon tipped drawing pen. The other image shows the difference in style produced by the two pens.