google.com/flights/

or from the US google.com/flights

via
money.cnn.com/2011/09/13/techn ...

and
insidesearch.blogspot.com/2011 ...

Ooops
insidesearch.blogspot.com/2011 ...

Hmm, I doubt this will become available outside the US, a pity though, cause it looks pretty solid.