The number one most elegant bicycle component is the ball bearing.
Photo taken while overhauling a hub this morning. Purity of form, perfection of function, lasts for decades with regular servicing, and a finish at least two orders of magnitude finer than anything else on a bike. My favorite are the 1/4" bearings in a classic bottom bracket, they make the others seem undersize.
The runner-up in this category, the humble and utilitarian bushing, gets points for simplicity but is a distant second in every other way.
My second favorite component are these old Sun Ringle peace-sign cable hangers.
(Imagine I trimmed my cable a millimeter shorter and wasn't missing one set screw.)
Simple, functional, beautiful, and playful. The arms follow the cable runs, the circle holds it all together, and the whole thing is a peace symbol! And it's purple! These cable hangers are also a great example of the affordances of CNC manufacturing, they would be absurdly difficult to make with manual machine tools. Shout out to tri-align style cantilever brakes too, mine are a tektro knockoff of the avid design, I love them.
Third favorite component is cotton bar tape.
To me, all other bar tape feels terrible, and only gets worse as it degrades. Cotton tape feels great immediately, and ages and weathers beautifully. The harlequin wrap above is a mix of Zefal and Newbaums (my LBS stocks Newbaums in many colors, but not black, and Zefal only in black
) but my favorite is the thick Velo-Orange stuff.
Possibly this preference has something to do with climate, the heat and humidity in New Orleans make foam rubber and vinyl often unpleasant to touch, and does leather no favors.
I'll have to think more about the next four!