[plestik]

There's also PlaneFinder: http://planefinder.net/ And CasperFlights (I'm the Flash developer for this one): http://casperflights.com

To be honest, I think Planefinder is the most impressive at the moment, their data is very, very good and their client is pretty decent as well.

[soult]

It seems all 3 sites use ADS-B receivers as source, so the only measurement in data quality is how many receivers they have and where they are.

I wasn't able to test your Flash software (Flash won't work on my computer), but since you seem to cater to plane spotters mostly: It would be cool to have your data combined with LiveATC.net so that I can see which planes are near an airport and what their pilots are saying.

[notahacker]

http://www.flightglobal.com/atlas too