First I'll start with some of the Americans:
The American Airlines fleet: First a 767-300 in the new livery:

N378AN America Airlines B763 at Heathrow EGLL by AeroPics, on Flickr
A 777-200

N788AN American Airlines B772 at Heathrow EGLL by AeroPics, on Flickr
And the AA 777-300ER departing Runway 27L:

N717AN American Airlines B77W at Heathrow EGLL by AeroPics, on Flickr
An old school AA 767:

N390AA American Airlines B763 at Heathrow EGLL by AeroPics, on Flickr
Old school United:

N648UA United Airlines B763 at Heathrow EGLL by AeroPics, on Flickr
And the 'new' United:

N776UA United Airlines B772 at Heathrow EGLL by AeroPics, on Flickr
Delta 767-300ER

N174DZ Delta Airlines B763 at Heathrow EGLL by AeroPics, on Flickr
Delta 767-400ER

N843MH Delta Airlines B764 at Heathrow EGLL by AeroPics, on Flickr
Next, American allies - an El Al 747 which has previously evaded me!

4X-ELB El Al B744 at Heathrow EGLL by AeroPics, on Flickr
Moving away, now a very nice (and very new) TAM 767:

PT-MSX TAM B763 at Heathrow EGLL by AeroPics, on Flickr
Now some 787s - managed to miss the BA ones both times!
First visit to Heathrow for Qatar's latest newsest 787 (at least at the time!)

AC-BCF Qatar Airways B788 at Heathrow EGLL by AeroPics, on Flickr
China Southern (very nice livery):

B-2725 China Southern B788 at Heathrow EGLL by AeroPics, on Flickr
Followed in by the Air India 787 from Delhi. The 777-300ER flight from Mumbai will also be replaced by the 787 next year:

VT-ANN Air India B788 at Heathrow EGLL by AeroPics, on Flickr