With airplanes spewing more than 600 million tons of carbon annually, cruising at 20,000 feet isn't the most eco-sensible way to go.  But you can make wiser choices by learning about which airlines have the most eco friendly practices.  For example: Delta flight attendants initiated an on-board recycling program at a few hubs that will expand to all domestic flights by the end of 2008; British Airways has saved 50,000 tons of C02 over two years by flying shorter, more direct international routes; Virgin Atlantic is investing all profits for 10 years in programs to develop renewable energy technologies and recently conducted a test flight using biofuels; and Icelandair is hosting a free concert headlined by Björk in Reykjavik this summer to raise environmental awareness.