The first that comes to mind is the Napoleonic expedition to Egypt. From Jacques Barzun's From Dawn to Decadence:

Their average age was 25. The oldest, the mathematician Monge, whom Bonaparte had befriended, was twice that age, and he shared with his friend Berthollet, a chemist, the lead in most operations. The youngest, not quite 15, was one of a half dozen students from the Polytechnic School, with as many again of its faculty and 33 of its alumni. The rest were: physicists, chemists, engineers, botanists and zoologists, geologists, physicians and pharmacologists, architects, painters, poets, musicians (one of them a musicologist), and a master printer on the supporting staff.

Some of the more famous savants on the expedition were the mathematician Joseph Fourier and the biologist Geoffrey Saint-Hilaire, who influenced Lamarck. The result was the Description of Egypt—20 huge volumes of illustrations and text—and the discovery of new species, advances in chemistry, geology, geography, and mathematics, and increased understanding of ancient Egyptian civilization, climaxing in the founding of modern Egyptology and the unearthing of the Rosetta stone.

Not a project per se, but the Solvay Conference was a meeting of all the greatest scientific minds of the early 20th century. There were 17 future nobel laureates in attendance. The list of names doubles a list of credits for every high school physics textbook for the last 50 years.

In 1944, the Bretton Woods Conference effectively decided what the international economy would look like after WWII. It ended up being quite important to the way money and international banking are handled today, and they established part of the IMF at that point. In my experience, few people are familiar with the event, but it was key in the creation of our current way of life.

Ninja edit: fixed link

Off top of my head NASA during the 60s, for physicists, chemists, aerospace and material science engineers, rocket scientists, etc, with the most notable result being the Apollo missions.

The NSA is probably the best contemporary example, employing a huge number of extremely intelligent mathematicians in encryption, sigint and computer science research, somewhere between hundreds and thousands, though the exact number is classified, as is exactly what they are doing.

I suppose a case could also be made for Shockley Semiconductor Labs in 1957. The Traitorous Eight, as well as Shockley himself, represented a large portion of the world's semiconductor expertise at the time, and said concentration of experts basically defined the corporate landscape of the electronics and software industry in the latter half of the twentieth century.

EDIT: In terms of output, the Muckers at Edison's lab in Menlo Park from the 1870s to the 1890s should probably be mentioned as well, as said lab was basically the first thing that could be described as a modern R&D department, and the output of intellectual property was prolific in both quantity and novelty.

Probably the greatest in literary history is the translation of the King James Bible. It was translated by a committee of 47 men, mostly top clergy, from Greek, Hebrew and Aramaic. The resulting work has been highly praised for its literary quality and had significant impact on the development of English literature and language. We owe to it, and more specifically its translators, the phrases 'grapes of wrath', 'sign of the times', 'no peace for the wicked', and many more.

In 1899 Edward Harriman sponsored a scientific expedition up to Alaska featuring more than 20 of America's most famous scientists at the time to explore and document the Alaskan Coast. From Timothy Egan's Short Nights of the Shadow Catcher:

Among those sailing north were the two best-known naturalists in America, John Muir and John Burroughs, both long-bearded and long-winded, called "the Two Johnnies." Also on board was a lanky gentleman with faraway eyes whose name was constantly in the papers: Gifford Pinchot, a man of the woods, from a wealthy family. At night, the ship's salon hosted arcane discussions by the scientists, speaking mostly in Latin, "fearfully and wonderfully learned," as Burroughs put it. The German-born forester Bernhard Fernow played Beethoven on the grand piano. Pinchot went on at length about how the outdoors made him feel most alive. The Two Johnnies argued, a flutter of white beards and spokes of fingers poking each other's chests. By day, the scientists would disembark in a particular bay, and then bring back all sorts of plants, fish, and wildlife to the ship, where they were picked apart. The Elder steamed past the rainforest shores of southeast Alaska, up into Glacier Bay, through the inlets of Prince William Sound, out along the far edge of the Aleutian Islands, touching the Siberian and then back, a nine-thousand-mile round-trip. No junket, the expedition claimed to have discovered six hundred species new to science, putting some of the best minds of new-century America to good use

Alfred Whitehead and Bertrand Russell, two of the most known and important mathematicians* of their time (late 19th, early 20th century) collaborated closely in order to come up with a set of axioms and inference rules in symbolic logic with which all mathematical truths could be proven.

They produced "Principia Mathematica", a three volume work on the foundation of mathematics published in 1910, 1912 and 1913. In 1927 appeared a second edition. Although the book was published, it ended in a disaster.

*B. Russell was also a philosopher.

In the late 1700's, the duke of Saxe-Coburg brought Goethe and Schiller and Herder and Wieland to the small town of Weimar. Which made the Weimar theater the most influential theater in Germany, and which generally had a tremendous impact on German literature.

The capital of Germany was moved to Weimar after WWI because of its history as a center for art and literature.

The Manhattan Project was a structured collaboration by the world's top physicists which was sustained towards a single objective and received massive funding, while simultaneously (some would say primarily) creating an industry. (Think about it - the manhattan project, didn't advance theory so much)

It's difficult to hit all the parameters.

Certain Big Science projects are amenable to large number of collaborators. eg High energy physics, (CERN/LHC), astronomy (eg SKA ) or biology (Human Genome Project.)

In a different direction, the Solvay conferences were meetings of the world's top physicists; for sheer concentrated starpower, the 5th Solvay conference is hard to beat.

Similar order of magnitude budgets as the Manhattan Project (MP) have been dedicated to Apollo and ITER (0.11 MP) though with less glamour quotient and recognition for individual scientists.