One that I use a lot is
www.aeroplanner.com
It is primary US-centric but there appears to be some limited non-US data. For instance, try doing a SmartChart and typing in EGLL as the airport ID.
Perhaps if enough of us pressure tham, they will increase their non-US coverage. They do seem to be quite responsive to customer requests.
[This message has been edited by BayAreaLondoner (edited 26 June 2001).]