Glenn Erickson, the mind and voice of DVD Savant, recently posted his thoughts at film.com on the lost art of the fight scene in modern-day movie making. I agree with most of his sentiments (while The Dark Knight has much to recommend it, the action sequences are confusing and impossible to follow - I dare anyone to keep up with the opening conflict in the parking deck upon a first viewing), and his six choices for classic movie "fights."
My addition to his list of classics comes from the obscure 1980 thriller Defiance, with Jan Michael-Vincent. I caught this at the Bright Leaf Drive-In on a double bill and recall little of the plot (something about a gang of hoods trying to drive Danny Aiello and other hapless cast members out of their apartment building), but vividly remember the climatic brutal battle between Vincent's ex-marine and the head of the gang.
My friends and myself were amazed at how "realistic" it seemed when compared to most movie fights. The two were bloodied, uncivilized, and used an array of unsporting-like and simply mean techniques as they bashed each other ... even staying entangled down a flight of stairs. To this day, I can't think of being impacted by any other filmed fight in such a manner. Highly recommended, and worth tracking down for a look (which sadly is not on DVD, but readily available via bootleg).