In my opinion the greatest losing effort in history was Seattle Slew in the 1978 Jockey Club Gold Cup. How he ran the opening half mile in :45.1 (with some colt named Affirmed pushing him all the way), and still had enough left in the tank to battle a 10-time G1 winner in Exceller down to the wire in a 12f race is beyond me. If you have never seen the race you should definitely watch it, and even if you have seen it 20 times......you should watch it again.
Here it is:
http://www.youtube.com/results?searc...&search=Search