Mystery Men.
The Unforgiven.
Ronin.
The Sting.
Willow.
The Princess Bride.
Eliminators.
I can’t imagine a better film for your purposes than Apollo 13. I once worked for a VP that wanted everyone in the company to see this film, solely for the lessons it held in team building and problem solving. I hafta say, I think he was right.
The guys on the ground and in space spontaneously form teams and solve extraordinary problems, under the strictest of deadlines and under unbelievable pressure. Not only do they come up with creative solutions, but they actually work and lives are saved. What’s more…it actually happened. Yeah, maybe Opie put some Hollywood into it, but still…
Apollo 13 is almost perfect; the only problem is that it involved already established teams doing problem solving. In other words, there was a lot of team activity, but very little team building.
Taking a ragtag bunch of mos and forging a team? Armagedon certainly fits the bill. Ah, just thought of a better one: The Right Stuff. That could have been named Team Building 101.
Something about space travel and sports makes them the best team building genres.
Major League, as noted, is a great example of team building.
I hesitate to mention it, but The Postman has a fair amount of team building going on. Assuming you don’t fall asleep before you get to it.
Miracle is too schmaltzy for me, but along those same lines maybe The Mighty Ducks.
Trading Places is a movie about unlikely people forming an unlikely team and prospering from it.
Also, it has boobies.
Reservoir Dogs - A team of perfect strangers must quickly come together for a project.
I can tell that you haven’t been to nearly enough boring, soul crushing team building seminars. Team building is an ongoing process and any team progresses through stages. While the teams at NASA and in space are pretty far advanced, the change in roles of the Bacon and Sinise charachters adds a interesting wrinkle to the development of the teams.
Oh, and by the way…this lesson costs $500. I accept bank checks and pay pal only. 
Howzabout Stand By Me, the one with Edward James Olmos and the inner-city calculus class?
I think you’re referring to “Stand and Deliver”. “Stand By Me” is the one about the four kids going to find the dead body (based on the Stephen King story).
I still consider “The Great Escape” to be a great “team” movie regardless of how many actually escaped Germany. I think the bigger feat was getting that many out of the POW camp (as in “prisoner”), and all the logistics and different problems that needed solving just to accomplish that. As was also mentioned, it was just as desirable a goal to cause the Germans to spend manpower and energy by chasing the escaped POWs as it was to actually get any of the POWs free. So as a team effort, it was very much a success.