Well, some great suggestions here guys, and much appreciated - I just threw North Dallas Forty on the queue. A few points of opinionated contention:
The Longest Yard is the one football movie that I own, and it's a classic flick. The thing about it is, I'm not sure whether it's a good football movie with a cool jail subplot, or a good jail movie with a cool football subplot. I think it's the latter, but I guess you could say the same about a lot of sports movies.
Major League as the best sports movie of all time?! It's a fun flick, but speaking very conservatively, there have to be upwards of half a dozen movies that would go ahead of it without a second thought. Best sports movie of all time: Hoosiers, in a landslide.
Necessary Roughness and The Replacements are at best a passable couple of hours each - the football equivalents of Cocktail. Yeah, they've got some hot girls and some wacky characters (as do 90% of movies). But when you look at a football movie and you see Keanu Reeves as the star QB, or Kathy Ireland as the hot but surprisingly good placekicker, well you need look no farther to ascertain the quality of that film. The Replacements was so bad, Gene Hackman's performance had postage all over it.
Rudy...a nice story, but I just can't get over how annoying the actor is who played Rudy. You just don't put an actor with an annoyingly dorky manner as your main character in a football movie. It's as if someone did "The Adam Taliafaro Story", starring...Urkle!