Stand on Zanzibar was the first of four novels that Brunner wrote that changed the way we looked at science fiction, because they presented crowded, clotted worlds where the background was as important and as fully realised as anything in the foreground.
The Jagged Orbit is set in a future America where racial tensions are at breaking point, and a major corporation is busy trying to sell arms to both sides at once, fomenting war in order to improve their business. It won the BSFA Award.
The Sheep Look Up is another dystopia, this time concerned with damage to the environment. At a time when corporations effectively control the government of the United States, pollution has got so bad that it results in poor health, poor sanitation, poor food supply and, eventually, civil unrest.
The Shockwave Rider is recognised as one of the ancestors of cyberpunk, it is also the novel that introduced the idea of a computer virus, though in the novel it is called a "worm". It is a novel about future shock, in which a programming genius uses his computer skills to go on the run in a world dominated by computer surveillance.
For other novels that confront issues of overpopulation, you should also check out The World Inside by Robert Silverberg, in which people live in three kilometre high tower blocks where order is only maintained by everyone sharing everything, including sex (it is considered a crime to refuse any invitation for sex). It's a brilliant picture of a very disturbing world.
Another classic of overpopulation is Make Room! Make Room!by Harry Harrison (which was filmed as Soylent Green). It's set in a future New York that is so crowded that water and food are in ever shorter supply, people have to share single room apartments, and theft and rioting are daily events.
Another novel that makes brilliant use of John Dos Passos's structure is 2312 by Kim Stanley Robinson. Using extracts from science journals, political journalism, history books and more, Robinson creates an extraordinarily vivid picture of everyday life three centuries from now when humanity has spread out across the solar system but the Earth is suffering from ecological collapse. The immediacy of the technique really makes it feel like we are there in the city that rolls around Mercury on rails, or in the hollowed-out asteroids that travel between the planets, or when long-extinct animals are returned to earth. 2312 won the Nebula Award.