Anything by Rogue Amoeba. I’m not sure there’s anything “clever” about the design they choose for their apps. They’re nice to interact with, they do the obvious thing and they’re well engineered (rarely crash, don’t have memory leaks, etc).
Reeder 2. The one thing it had that other RSS apps didn’t have is collapsable columns. Accounts was the leftmost column. When you selected an account, it would collapse to the width of a small icon. The next columns is the RSS feeds, which would do the same. This left you just only the list of news items and the viewer taking up most of the space. Screen real estate is less of an issue in this day and age of 4k screens, so they removed this particular feature, but I always appreciated it.
DaisyDisk. Again, nothing clever, just a beautiful interface that always works and always does what you expect it to. I wish it was a little faster, like WizTree, but that might have more to do with HFS+ than the app itself.
Quicksilver. It’s mostly been replaced by Alfred at this point, but there were things you could do with Quicksilver that you can’t do with Alfred, such as chaining files, actions and apps together on the fly. I think you can do something similar in Alfred with Workflows, but you have to set it up ahead of time. Quicksilver had a set of built in actions that would let you do a surprising number of things on the fly, like open an application in AppZapper.
AppZapper. I don’t know if this one qualifies as a “big name” or not, but it’s always the first app I install on a new Mac.