Like Smash first mentioned, I've never built a Nuclear Plant, except in testing. It just comes too late in the game, and I've already solved production and pollution issues by then.
A close second is the SAAM. They are simply not necessary in games vs. the AI... CMs don't slam into your cities, and fighters (and sometimes AEGIS) can protect cities just fine.
The Courthouse originally suggested is one of my own most heavily used improvements, esp. if I must spend time at Monarchy or Republic. Courthouse are how I get my fringe cities to grow in a Republic (WLTC days).
As for the Recycling Plant... my opinions about it have changed now that I don't allow wild nuclear wars. Since they are so cheap to both build and maintain, plus available earlier, any city that can exceed 41 shields production, but will never exceed a production of 61 shields gets one permanently. I don't replace it with Solar later on. But Solar does have 2 advantages: It can take the place of Power/Hydro/Nuclear to give the 50% production bonus, and it will nullify half a polluted square's contribution to global warming computations. Since I always have the Hoover Dam by Environmentalism, the first point is moot. Since I don't create 200+ polluted squares in a nuclear war anymore, the second is moot... ergo, only cities that exceed 61 shield capacity get Solar Plants.
As for Granaries, that could easily be a 10,000 character post to describe the many circumstances of how they can be useful, particularly in late game when going for large scores. But most Civ II players will obtain the Pyramids (build or capture). In some games, it might be a while until you can capture the Pyramids, and Granaries are particularly useful in cities that are cranking out settlers, and in the SSC to ensure the food reserve for max-effort days with scientists.
