The maker of the TGV  begins initial deliveries of the next-generation superfast train, the AGV, in 2010. Far more energy efficient than its forebear, the AGV is a miracle of engineering, capable of speeds of 225 miles per hour. It promises to dominate the rapidly expanding European market for high-speed rail , which is intended to replace short-haul flights and their hefty carbon footprints. Top 50: No. 45 
No company has changed America's relationship with driving more than Zipcar , which was founded by urban-planning geeks aiming to reduce carbon emissions. By providing urbanites with access to cars, the company has made city living more attractive to people who would otherwise own them. And cities are the best tool we have to trim per capita greenhouse-gas emissions; residents have far smaller carbon footprints than suburbanites. Zipcar is also partnering with Zimride to promote ride sharing. The company announced its first quarterly profit in June 2009 and plans an IPO in 2010.
3. STX Europe
The Oslo-based shipbuilder built the giant that is the Oasis of the Seas . Say what you will about the aesthetics of the thing , the mega-cruise-ship is a feat of engineering and innovation. STX is also building icebreakers, which will be needed for the Northwest Passage through the Arctic.
The industrial conglomerate has a head start on the next big thing in air-traffic control: GPS-enabled flight. SmartPath , the all-digital GPS landing system from Honeywell's aerospace arm, is the only such ground-based system, and the potential market is huge. The technology promises to reduce congestion and save airlines billions of dollars.
Known for its trains, propeller planes, and small jets for companies and regional airlines, Bombardier  has won a huge contract for China's massive high-speed-rail expansion. The company is also challenging Boeing and Airbus with its new C-series of larger single-aisle jets, scheduled for delivery in 2013.
The lithium-ion ferrous phosphate battery that the Chinese company has developed for its E6 all-electric sedan has three major advantages over standard lithium-ion batteries: it costs half as much, lasts longer, and uses a nontoxic fluid. BYD  plans to bring the E6 to market this year. Top 50: No.16 
The German conglomerate's Siemens Mobility unit leads the light-rail expansion in the U.S., with the bulk of the business in Sacramento, Salt Lake, and Denver, among others. Munich recently awarded the company a major contract for an innovative new parking-space management system. And it is introducing the greenest-ever traffic-light technology, which use as much as 90% less power than standard lights.
The computer giant  has quietly become a dominant force in developing technology for smart traffic management and congestion pricing, two issues that will be key to any workable city plan that's both green and scalable. Its tests in Stockholm were key in getting the city designated as the European Green Capital for 2010. Top 50 No. 18 
9. ITA Software
Whether you book airline tickets online through, say, Continental Airlines or Kayak, United or Orbitz, chances are good that you'll be using ITA software. The company is behind 65% of online airline bookings.
10. Fisker Automotive
Last October, the maker of the high-style-and high-priced-Karma plug-in hybrid  sports car announced that it would acquire and retool a closed GM plant in Delaware to produce the Nina , a family-sized electric car, using a $528.7 million loan from the Department of Energy. The Nina is expected to cost about half as much as the $80,000-plus Karma. http://www.fastcompany.com/tag/fisker-nina