Kaweco Brass Sport

The Brass Sport takes the Sport pocket pen, and hardens it for a tough life (like the AL Sport) and then makes it really heavy and lovely. They're made from brass, so they can withstand really heavy use, while looking great. As with the rest of the Sport range, they fit neatly in a pocket, but posting the cap on the back makes them a nice size to write with too.

If you want something even more uncompromisingly pocketable, and just as brassy, have a look at the Kaweco Liliput - tiny metal pocket pens.