The Monteverde Tool Pen is one of the best geeky pens I've ever seen. Not only is it a wonderfully made Monteverde fountain pen, it's also a ruler, a level, a stylus, and a screwdriver!
This pen takes standard international cartridges, and can be made to use the Monteverde Mini Converter if you clip part of the end of the plunger off. That's what I've done to this pen here, which belongs to my girlfriend Kelly.
The pen comes in four colors, silver, yellow, black, and red, which is a special edition from the Goulet Pen Company.
It's only available with a Medium nib, but it's a #5 nib which is easily swapped with any other #5 nib.
If you're interested in getting one of these, all four colors are available from Goulet at this link, for a reasonable $40. You also get a free pack of black cartridges, which is pretty nice.
I'm actually waiting on a new nib to get in for this particular pen. Kelly wants it to write a bit finer, so I'm gonna swap the nibs out, and smooth the new one to write how she wants.
Ink used is Noodler's X-Feather, which behaves fantastically on cheap paper, and is the darkest, truest black ink I've seen.
Paper is a Rhodia 12 pad.