the pen and the man
I am a functionalist, so most of the time function takes precedence over form (much to the annoyance of some close ones :X). I carry a Pilot BP145 retractable ballpoint pen with me. Simple, low profile, plastic, but writes smoothly. It costs below $5 and you won't cry if you drop it on the floor accidentally. (the colleague screamed when his maid used his dunno Mont Blanc or Waterman to take memo). As for presentation (no, not powerpoint), I'm not sure if it helps to carry an expensive pen but have uncut dirty fingernails and unshined shoes.
But I must say the choice of pen is important for my previous job when the tip of your pen spends more time on the paper than you lying on the bed. Highly recommend Jetscream from Uni :) Used to be a big fan of Mitsubishi Pencil.