I stumbled across the MC34063 as a "classic" switching regulator (considered somewhat obsolete today because of the low, 100 kHz switching frequency). It was news to me. But still not bad, at $0.61 each at Mouser.
Now I'm wondering what else is considered a classic, for example, the 555, 2N2222, LM317, LM386, etc.
If it's still around forty years later, then it has to be "classic". Lots of ICs have been introduced over the decades, but either they ended up with little application, or the need changed. A lot of linear ICs have gone out of production because design has changed. The more specialized something is, the more likely it has a limited run. The more open an IC is, the more likely it will continue to exist. There's always need for audio amplifiers, the 555 can be used for all kinds of things. An IC useful in the days of analog tv might find secondary uses, but often those were not so accessible so using them for other things meant limitations, and now that there's no more analog tv, such ICs will disappear if they haven't already.
When I was buying some ICs - both TH and SMD - at a shop in New Delhi last year, the shop owner was so incredibly inept that I had a hard time hiding my irritation. Another customer chose that moment to walk in, looked at the items already on the counter, sniffed disdainfully and said "Do people still use these things?" I gave him an earful about how the latest microprocessors and MCUs are not always the best solution for everything. He quickly backed off, which was fortunate because I might have punched him if he hadn't.
That depends on how you define "classic". Take any given person, find out what was available when they started as a hobbyist or a wet-behind-the- ears engineer, and chances are high that you've found their "classic".
** Most of the 79xx and 79xx voltage regulators from the late 70s are still heavily used.
The most common high performance, low noise op-amp used in audio is the Signetics NE5532 from circa 1976 - SMD versions are used by the million each year.
The Texas Instruments TLxxx series of Bi-FET op-amps is similarly popular, released in 1977.
But all of these pale when compared to the 6L6 valve, released by RCA in 1936 and still in mass production in several factors in China and Russia with almost all sold to the West for use in instrument amplifiers.
I think those classify as "antique" rather than "classic".
The 709 was kind of dated by the time many of us learned about it. Though in the later half of the seventies, one magazine article used some 709s, they needed some voltage limiting on audio signals, and the 709 offered up suitable diodes at the input (or something like that). The 709 wasn't used as an opamp, just those diodes, the rest of the device wasn't connected.
I still use the 78xx, 79xx, NE5532 & TL7x myself. Regarding valves, the 12AX7/ECC83 is still very much the rage among guitarists, perhaps more so than the 6L6 because many talented guitarists cannot afford an all-tube amp and have to be content with a 12AX7 in the preamp.
I had one of that generation. SOmeone gave it to me, but I cant' remember if I filed it away somewhere, or I actually discarded it.
Yes, the 741 still has some value, while the 709 didnt' generally offer as much, yet needed the compensation.
I have some 702s around, got in a box of junk decades ago, and those were odd (assuming I am remembering the number right). Less the universal device that opamps became.
I think the case can be made that there were some very important devices that were bold when released, and are worthy of remembering, but they weren't so great that they continued to be used. A 555 keeps on being used, the 709 was important but superceded by other devices (which in turn were superceded by others).
One great thing about op-amps is that they have generally kept the same pinout (well within package type).
Some genuinely ground-breaking chips are still sold, such as the LM309, which introduced the band-gap reference. It was also a classic Bob Widlar prank.
(Of course they're ridiculously expensive, and used only for repairs, but they're still being made.)
Another example is the LM306 comparator.
The uA709 isn't made any more, of course, but you can get LM301s for cheap.
Some of my faves were discontinued over the years, including the MAX900 comparator, the TL011 series current mirrors, the AD639 trigonometric converter, and the VTC VA713 75 MHz operational transconductance amplifier. (Sort of an LM13700 on steroids.)