I've carried a Fisher Space Pen Bullet on and off since I was a kid. ("Write underwater and upside down!") I usually lose them in a matter of weeks, but while I can manage to hold on to one I do appreciate its minimalist design, small size, and great "fiddleability." Of course, the Space Pen is surrounded by some epic marketing and myth. Did NASA really invest millions to develop a perfect pen for astronauts? No, apparently, Fisher had developed the pen technology and later brought it to NASA. Following two years of testing, the space agency bought 400 of the pens at a 40 percent discount. And on October 11, 1968, Apollo 7 astronauts carried Fisher Space Pens, model AG7, into orbit.
Fisher Space Pen AG7 (Amazon)