An open-source design of the N900s stylus for one of the best open-source phones out there ;-)

Compared to the original this model is slightly more edgy but this simplifies printing and gives a little more room for creating a nice finish.

I've included the Blender source so you can modify the pen as you like.

Update:

A word of warning: Since i had to take my measurements of a few pictures a friend of mine took of his original (because i lost mine long ago) i cannot guarantee sub-millimeter accuracy. Plastic parts are easy to modify after printing for making them fit but aluminum and alike are not, please keep that in mind.

One more thing... If you take the .stl and it's just about a cm in length and too narrow to print: Simply scale it up 10 times equally in every dimension. The length should be 9.9cm.