Well there are lots of lovely components. LEDs are pretty but not as magic as a nice glowing valve, especially when it gets a blue glow as well. Op-amps are great, but my feelings for them are marred by early experience with unstable and temperamental ones. And getting electric shocks from big inductors was exciting. Transistors were amazing when I first got those - though so boring to look at and so confusing when they got NPN and PNP (I still get mixed up! But valves, you could SEE the electrons going from cathode to anode).
But the single component that has to be top is the 555. From the first one it always did exactly what it said on the box - and lots more beside. I can't think of another specific numbered component that I've used continuously from when it became available to the present day. I suppose the 10k resistor might be a runner, but if it disappeared overnight, I could happily substitute another value. What would we do without the 555? (Use microcontrollers for everything I expect.) Its about the only chip that I look at the internal circuit and wonder how else I can use those subcircuits.
Just a shame you grouped them with other chips. Yes many of them are very good, but is any as unique as the 555?