Atomic Systems

I found this site over a year ago, it lets you track flights over the US and leaving the UK.
http://www.aeroseek.com/webtrax/fboweb.html

My wife is currently somewhere over Newfoundland - looks like quite an exciting flight - 35,000ft to sea level and back

Looks like they might be experiencing some turbulence!

There's also this one at http://www.openatc.com/ although it doesn't show every single flight unfortunately.