The best pens I have ever used were a brand called "Stylist" pens. The architect's office where I used to work used them almost exclusively. They are like a Cross between a felt-tip and a Sharpie, but more durable than a felt-tip and they don't bleed as much as a Sharpie. They also come in tons of neat colors (burgundy, lavender, sky...) They gave me a box of them when I left (I often expressed my love for the Stylists) and I'm almost out. <sob>

I think I like them so much because I just feel so... professional using them. Anything I write or draw with them seems that much more polished. Purely psychological, I'm sure. It was my first job out of college and will always be equated with professionalism in my mind.