There are several Michael Artaud pens that probably would vie for the #1 slot. As well there are some art pens out there that seem to be made more to shock than to write with.
The Blood Pen, invented by Bob Partington, is a must-have accessory for any respectable vampire writer.
I know some of you have seen the Blood Pen ever since early 2008, but I just found it today and had to post some photos of it here. This creepy gadget features a syringe and a pen nib, connected by a plastic mechanism. After you fill the syringe with your own blood (seems reasonable enough), you stick it in place and start writing your bloody memoirs.
As you can see in the video at the bottom, it’s not the best writing tool, as it often drips more blood than you’d like, but the idea in itself is enough to impress you. I don’t much like the flashy silver feather attached, but I guess that’s just a matter of taste.