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Challenging traditional notions of what tall buildings are supposed to look like, developers around the world have unveiled a flurry of new skyscraper designs in the past few months.

A tower in China owned by a tobacco company is shaped like a cigarette pack and will breathe in air to push turbines that will power the entire building. A plan for a tripartite spire in Moscow aims to be not only the tallest building in Europe, but also the only modern skyscraper with a natural ventilation system. Another design, in Louisville, Ky., looks like a three-legged chair with a 22-story diagonal elevator that accesses a "floating island in the sky" art museum.

To some big-building watchers, the over-the-top swoops and curves reflect a top-of-the-market mentality as global real-estate tycoons pour money into notoriously difficult-to-build stylized symbols of ego and economic strength. "Skyscrapers are always a function of good economic times," says Carol Willis, founder of New York's Skyscraper Museum.

The good times include a robust and global high-end residential market in major cosmopolitan cities. For the first time, many of the tallest buildings being built include apartments for the well-heeled. Strong economies in Asia and the U.S., as well as oil-fueled booms in the Middle East and Russia, are also driving the soaring spectacles.

A flush market has made often risk-averse, contractors more willing to take the plunge on a project that doesn't look like anything they have built before. "The big contractors are becoming more adventurous, going for a challenge," says David Scott, a skyscraper engineer with the London-based firm Arup and chairman of the Council on Tall Buildings and Urban Habitat, a sort of skyscraper-designer trade group.

Advancements in design technology, construction techniques and steel and concrete fabrication also give the financiers shelling out for these symbols in the sky a little more leeway in paying for pizzazz. The island part of Louisville's Museum Plaza, for example, will be built at ground level and lifted 220 feet with the type of massive jacks that have been used to install weighty retractable roofs on football stadiums.

The shimmering Moscow City Tower, in the Russian capital's planned financial district, would rise from an unusual Y-shaped base into narrow blades that taper as they reach 118 stories -- nearly 2,000 feet -- above the ground. The tower, which has been dubbed by its developer, STT Group, a "vertical city for 25,000 people," will include apartments, a hotel, offices and leisure space. It is expected to cost $1.5 billion and be completed as early as 2010.

The architects, London-based Foster & Partners, led by Norman Foster, say it will be the world's tallest "naturally ventilated" tower, reducing heating demands in frigid Moscow winters by 20%. Rain and snow harvesting will supply 30% of the water for sinks and toilets.

In Guangzhou, China, state-owned China National Tobacco Co. Guangdong's new headquarters will be an undulating rectangle. It won't be the tallest in town, but it is aiming for a lofty goal: having zero net impact on energy consumption. Gill-like gaps in the facade will "inhale" wind that will propel turbines to produce electricity.

A tobacco-company icon inhaling air as a way to clean the environment? "It is ironic, no question," says Thomas Kerwin, managing partner at the Chicago office of architects Skidmore, Owings & Merrill, which won a competition to design the tower. "But it's a very profitable company and in some ways, one could say they are trying to put their profits to good use." This is the first time a skyscraper will strive for full energy independence, he says. "Is it too ambitious a goal? One might say that, but it's something we should be striving to achieve."

He says making a tower green is a bigger challenge than making it tall, something Skidmore knows all about. It's also building the Burj Dubai, a residential condominium and hotel in Dubai, which is set to top 2,300 feet. The developer, Emaar Properties, won't divulge the actual height for fear that competitors will try to break it.

"Height doesn't seem to be a problem," says Mr. Kerwin. "Engineering feats are becoming commonplace. ... Pushing the envelope from a sustainability perspective is more difficult. We're still in relatively new territory. Systems aren't tested fully."

The most atypical skyscraper scheme out there is the Museum Plaza in Louisville, designed by Office for Metropolitan Architecture's New York branch. It could be mistaken for an agglomeration of several towers on stilts, connected in the middle by the three-story "island" 22 stories up. It will house a 50,000-square-foot contemporary-art museum and lobbies for offices, hotels and loft condominiums that will be perched in three finger-like towers that emerge from the top of the island. Visitors will access the island through an elevator that leans diagonally against the side of the building.

Joshua Prince-Ramus, the lead architect, says the plan was born from the "backwards" nature of the development. Instead of the commercial aspects driving the project, the museum is the main focus. The other moneymaking uses are there to support it. Physical constraints including a narrow site, a 15-foot-high flood wall that protects the area from the Ohio River and a massive electrical trunk line underneath the site forced Mr. Prince-Ramus to lift most of the building off the ground.

"It has a rawness, an awkwardness to it that's really beautiful -- like the gap between Lauren Hutton's teeth. It keeps your attention," says Mr. Prince-Ramus.

Museum Plaza is the brainchild of Laura Lee Brown and her husband, Steve Wilson, local contemporary-art aficionados and rural-space conservationists. The couple own a significant share of Brown-Forman Corp., maker of Jack Daniel's Whiskey and Southern Comfort.

The duo wanted a downtown space for modern art that would draw people into the city. To finance the $380 million project, they joined with hotel developer Steve Poe, who recently built a Marriott hotel in downtown Louisville, and Craig Greenberg, a local attorney. They also hope to get $80 million in tax increment financing from the city and state, which is supported by the mayor and governor.

For all the grand plans of these and other developers around the world, experience indicates many of the proposed projects will never break ground. The history of skyscraper design is littered with never-realized, stalled or half-completed projects. The Moscow City Tower is the second stab in recent years for a supertall structure there; the first never got off the ground for lack of financing.

The fate of Louisville's Museum Plaza will depend on a host of unknowns that include landing a hotel operator and residential and office tenants, who might prefer to be in more-traditional structures. China National Tobacco has better prospects since its developer also plans to occupy the building.

Once completed, tall buildings have a checkered past in terms of attracting tenants. The Twin Towers in New York were partially empty for years after construction and needed a state bailout to keep them solvent. The Empire State Building was nicknamed the "Empty State Building" for its inability to attract tenants.

A skyscraper under construction in China illustrates the challenges in making tall buildings a reality. Japanese developer Mori Building Co. unveiled the Shanghai World Financial Center in the mid-1990s. After a 1998 groundbreaking, work was halted because of the Asian financial crisis. Then the design, which included a circular void at the top to help stabilize the structure on windy days, irked the Chinese who thought it evoked the round sun of the Japanese flag. That caused further delays. After several redesigns, the circle became a trapezoid, and the building by New York architecture firm Kohn Pedersen Fox is finally rising out of the ground.

Ms. Willis of the Skyscraper Museum says the curves, bends and contortions of today's tall buildings echo a skyscraper boom -- and eventual bust -- in the late 1920s. While many famous spires went up before the 1929 stock-market crash, she says there were "many more announcements for the tallest building or eccentric designs, some brightly colored, that never got built."