A bunch of personal ballpoint pen drawings I did earlier this year, with a hint of light cream marker for tint. No underdrawing for most of them - just playing in my comfort zone! I find that adapting the design to compensate for small mistakes can often add interest.
I licensed most of them to the "Numenera" RPG universe, for use throughout their upcoming game books. It takes place a billion years in the future, within which 9 civilizations have risen and fallen. I love me a good high tech mystery artifact. :-)
Ballpoint is my favorite sketch medium because with a very light touch I can get the value to modulate like pencil, and yet it won't smudge.