Either modern or vintage, singularly it is the design that is unique to all others, has a great appeal and ultimately and unfortunately eventually becomes a icon copied by many other pen companies.
A few examples come to mind : Waterman Patrician
Oversize, a new modern unbreakable material, attractive elements of clip, cap bands and coin logo emblem at end of barrel.
Pelikan fountain pens
Curiously a unique style of simplicity that has been unchanged since concept for almost 100 years. Consistent shape and style of barrel, cap. The only variations have been colors and a few classic overlays such as the Toledo silverware. My M800 c1992
The Parker 51 - the most radical change in style and mechanics of a fountain pen. Shape, style, function and the most copied fountain pen in history.
a few of my "51's" - photo by Bill Reipl
Certainly there are many more pens that qualify as a "Classic"
Name a few and show what you may have