I'm not sure how many stories by Harry Harrison I read in my teen s.f. fiend phase but the two that made an impression were:
The first is a terrific bleak and gritty novel set in a near-future (our past, now: 1999) New York, when overpopulation and resource-depletion have made life pretty fucking miserable. That 1966 novel was then turned into a vastly inferior movie, Soylent Green, with absurd alterations to the plot. (In Make Room!, soylent is not "made of people", it's made of soya and lentils. That and krill and seaweed crackers make up the diet for 99 percent of the population).
The second is an entertaining alternative history set in a world dominated by the British Empire (which still controls North America - hence the NASA-level grandiosity of digging a railway tunnel to connect the motherland and the colonies).
Oddly this past year I bought and reread Make Room! Make Room! (still excellent, and it would lend itself to being made into a far more faithful movie in the current climate for dystopian and post-cataclysm film/TV: Hunger Games, Revolution, etc). And I bought but have yet to reread A Transatlantic Tunnel, Hurrah!. Odder still I also recently wrote (briefly) about HH in an article that looks at a bunch of things including steampunk, arguing that that 1972's Hurrah! (also known as Tunnel Through the Deeps) is an unacknowledged precursor of that genre: