I nominate the 1999 Whitney Hcp........Victory Gallop and Behrens.
This is just an amazing performance by both horses. The final time, 1:48.66, wasn't all that special, but the race itself was really one for the ages.
http://www.youtube.com/watch?v=Mf7UIKALfM8
Another one I thought was pretty amazing was Swept Overboard's win in the 2002 Met Mile....in 1:33.34. Couldn't find the race on Youtube.