Well, after the early 1970s, nothing. These days only the older steeds interest me. That said, from each decade (50s, 60s and 70s) my suggestion for most collectible would be a top dog Cinelli. I have never owned one, though, so cannot comment on how good they really are.
I would warn that seeking a specific something from a specific sometime might prove frustrating. In my case, I hunt and what I find is, way more often than not, not what I was looking for. An example would be a late sixties Raleigh Carlton. Not high end but wonderfully appealing, thanks in part, a big part, to the chrome plated head tube lugs. Though entry level, it will be fun to build and ride this bike but it is not anything special. Just a cool looking old bike...
Poor picture of the chrome lugs but it was the lug work that sold me on this bike that I got for free...
For me, my personal choices these days are the older steeds and ones that sport chrome plated socks, front and back, and chrome plated head tube lugs... I even like, really like, all chrome plated bikes, such as this entry level Torpado Luxe and check out the lug work...
1950s - Rabeneick 120d which I happen to have...
1964 Torpado Professional which I happen to have...
And a 1973 Peugeot PX10 0f which I have had two but none now. I might add that the Peugeot PX10 from the fifties, sixties and seventies is something special and, perhaps, iconic in nature...
As for the eighties???
There is a bit of a point here. Don't restrict your search. Doing so might mean that you miss out on something really really cool. That is what I have learned after many years of collecting and sharing of vintage road bicycles.