Are you still using 7400-Series Logic, if so, where?

Over the past several months, I have been learning about and repairing 8-bit computer and video game systems. So far, I have worked on the VIC-20, C64, ZX-81, Apple II, and have been learning about the TI 99/A.

It always amazes how much of these early computer systems were built almost entirely with standard 7400-series (LS and HC) chips.

Occasionally, I need to replace a 7400-series chip. (I always hope it is one of those and not one of the ASICs!) While looking for modern replacements, I have noticed the trend that they are becoming more scarce. The LS-series is almost entirely gone--and with good reason. While HC and HCT continue to be somewhat available, they are usually only available in surface-mount packages.

That leads me to the question: Who is still using the venerable 7400-series logic chips today?

To me, there are three groups that might be using them:

1. Learning. Students and hobbyist learning about digital logic
2. New Design. Hardware that needs glue-logic. Are these using multi-gate chips or the single-gate variants?
3. Repair. Older electronics in need of replacements. Here is where I mostly sit.

Do you fit into one of those categories? If not, where do you land?

And THEN, which chips are the must-have on-hand?

Obviously, the answer depends on how you might be using them. But, I'm curious to know how you use 7400-series chips and which ones would you keep in stock?