You didn't state a genre.
Are we talkin'
rock here?
Hmmm. Milestones ... Milestones.
You can't really talk about it in terms of "songs," because, ya' see, at the time, we had what are called "albums."

Just messin' with ya.
In the mid/late 60's I'd say "Pet Sounds" and "Sergeant Pepper" definitely set the tone for the era in terms of production value.
Something very significant happened at that time. A paradign shift in the way music was tracked mixed, mastered, etc. To try and get in to the specifics of it all would entail a much longer post than anyone has time for right now. But suffice it to say that those two records were big ... and the ability to multi-track for the first time was at the head of it, moreless.
In the 70's it would have to be Pink Floyd Dark Side of the Moon and basically everything else they did. Led Zepelin had some pretty stunning accomplishments as well, for the time. This was during an era where multi-track recording was mature, moreless, and people were really pushing it and exploring it's limits.
1980's ... ya got me.

Actually, that's a tough call, although I might lean a little towards the Police records as being standouts. Nothing leaps out at me, though, from that era as being truly "defining" in terms of production value. I'll have to think on it. There's probably something very obvious I'm missing. I look at the 80's as being a transitional period. Multi-tracking had reached it's maturity ... and digital recording was just being introduced. CD players very quickly became the standard, and it was an awkward transition in to digital, from both the recording side and the listening side.
And in the 90's we had Okay Computer by Radio Head, which I think has moreless set a new standard for rock records in the era of digital recording. Someone basically figured out, with this record, how to get the most out of what digital recoridng and mixing offered. In a way, the 90's represent a time when the digital and analog mediums came to a compromize, rather than one taking over the other. Same trend occured with tubes, transformers, and everything else we liked about the older recording technology. They became cool again, and we could appreciate them without having to totally revert back to them.
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