The eradication of smallpox springs to mind, for obvious reasons.

On a smaller scale, Notre Dame took between a hundred and two hundred years to complete, depending on where you draw the line around "complete." That's fairly typical for such constructions. Not just medieval ones, either; Sagrada Família broke ground in 1882 and was only consecrated in 2010, and it's still not done. (Leave aside the fact that it's *super-*creepy-looking.)

Smaller still, the famous pitch drop experiment was started in 1927. Many people are confused by this one, because they think it's a demonstration. It isn't. It's a for-realsies experiment, the goal of which is to empirically measure the viscosity of pitch. The longer the experiment goes on the better the estimate of that measurement, but the result will start to be meaningful once the experiment is around the hundred-year-old mark or so.

And then, of course … people have kids. That's the best example of all.

Certainly the Voyager Spacecraft has to fit into the scheme somewhere.

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I read a book on FDR that I can no longer remember the name of nor have in my possession. At one point, the book argued convincingly that FDR's Presidency ultimately had the long term effect of American economic and military security for reasons I will briefly outline here as best I can recall. By setting up the European economies so that they were able to become profitable, successful and grow and to America's lasting and mutual benefit, FDR enabled a following number of generations to enjoy the pleasures of an overall expanding economy(note: some economic crises were at this point realized to be not altogether unavoidable) and of a strong network of economic and military allies for decades. Before World War 2 (which, it should be noted here of all places, could very well have been avoided using more prudent planning, not least of which on the American side, and leads to the sometimes confusing foreign policy endeavors we have now) international politics are hardly a noon's shadow of what they are now and FDR laid the way for American hegemonic interaction in global politics as a means to avoid potentially unavoidable wars the likes of WW2. I think it is reasonable to say that we in the west have indeed benefited from these policies. I have to run, but maybe more tomorrow.