Rocky I, II, III, Ali, Raging Bull, The Fighter, The Great White Hope. Boxing films are the best sports films
Any Given Sunday is my favorite football movie. Remember the Titans is probably second, or maybe Brian's Song.
Basketball has a ton of awesome ones. White Men Can't Jump is my favorite, though not the 'best'. Space Jam da best. Also love He Got Game, Hoop Dreams (documentary), and Hoosiers
Favorite baseball movie = 61. The Sandlot, Bull Durnham, For the Love of the Game, Major League, Eight Men Out, and of course Money Ball are also awesome.
from other sports: Miracle, Kingpin (bowling counts)... that's all I got