FlightWise.com, with some help from Google, has just released a very nice KML that shows thousands of near real-time flights over the United States.

The data is roughly 15 to 20 minutes behind the current time, due to FAA restrictions. However, this is an excellent tool to get a look at all of the current flights in the US.
By hovering on a plane, you can see the flight number and a path of their journey to that point. Clicking on a plane gives you more information about the flight, including an option to view the full path of the flight as a KML tour. Opening the tour will show your plane with a larger red icon, and it will fly the entire path of its journey to that point.

For more information or to try it for yourself, you can:
• Read about it on the Google Lat Long Blog
• Try it using the Google Earth Plug-in
• Download the KML file for use in Google Earth
About Mickey Mellen
Mickey has been using Google Earth since it was released in 2005, and has created a variety of geo-related sites including Google Earth Hacks. He runs a web design firm in Marietta, GA, where he lives with his wife and two kids.
You might want to check out flightradar24.com as well. It uses a network of ADS-B receivers, a lot like AIS receivers that’s used on marinetraffic.com, so it’s pretty much real time.
This is wonderful. I have been waiting for something exactly like this for some time. My only complaint is the same as I have for the flightwise data in general – I want more! I wouldn’t like to see all international flights, not just those with an end in the United States.
Thanks for the heads up!
None right now.