I am surprised nobody has mentioned Flightradar24[0] yet. It displays planes on a Google Map with altitude, airline and flight path information. The data comes directly from ADS-B receivers of volunteers, so only planes with ADS-B transponder are shown and the coverage outside of Europe is spotty.
Living in the path of a mid-size airport this tool is great for identifying noisy airplane types.
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.
Living in the path of a mid-size airport this tool is great for identifying noisy airplane types.
0: http://www.flightradar24.com/