(1) Old school drafting pens, with 00 or 000 size tips -- Rapidograph, Kohinoor, Faber, and others
Pros -- fine lines, don't need to press, with film inks you can write on glass, or just about anything
Cons -- need special ink, cranky, leak if you take them on planes, drop them and you're out $20 for a new tip
got to wait for the ink to dry or it smears, getting harder and harder to find
(2) Fountain pen with XF nib
Pros -- fine lines, don't need to press, lots of ink colours and you can blend your own
Cons -- at least $60 - $80 for a good one, you can't let anyone else use it once you have it broken in
(3) Pentel Precise V5 and V7
Pros -- cheap! fine lines, reliable
Cons -- not as good as (1) or (2), but not as expensive, either