(Updated with new codes.)

AirTran, American Airlines, Delta Airlines and Virgin America have started offering WiFi internet on select flights through Gogo Inflight Internet. According to this thread on SlickDeals.net, you can try it out for free if you’re on a flight where it’s offered by following these instructions:

• On the flight, connect to the ‘gogoinflight’ wireless network.
• Open any webpage.
• Create a new Gogo account.
• On the payment info page, enter promo code 1669da59g1.

The above code expires September 30, 2009. For American Airlines, try code 1815rft3321 which expires October 31, 2009.