Grimes, having spent most of his time up till now trying not to soil himself, runs out into the middle of the street to take out a Technical with his grenade launcher while the enemy machine gunner frantically tries to reload his weapon. Oh, and he misses. So he reloads while out in the open and hits it dead on the second time.
Thomas being too scared to go back out at first, then saddling up and running out to rejoin the convoy just as it's rolling out again. (Truth in Television, as there was a Ranger who was just as scared to go back out, and jumped on just as Humvees were jumping back out).
Also, when the Delta operators silently take out an anti-tank gun crew using night vision goggles and garroting wire, then turn the gun on the buggers who've been making them so miserable till then.
The Delta snipers holding off (and killing) hordes of Somali militiamen.
Eversmann running out alone under heavy fire to mark the Somalis' position with an IR strobe. He did have covering fire, but it takes a lot of guts to run out into and under hundreds of guys trying to kill you.
In the book, when it became obvious that the convoy was getting shredded, and they wouldn't be able to reinforce either crash site, all the other soldiers stood up and prepared to go out to rescue them. The cooks, medics, technicians, supply officers... basically all the logistics people that would never expect to see front-line combat immediately answered the call to go out and rescue their brothers in arms.
Later in the film, Colonel McKnight is told that he and his men don't have to go back out to rescue the survivors. He gives the person telling him a long, level stare, as if daring him to say that again. The guy shuts up. Not only does he go back out, he has his lightly armored Humvee go to the front of the line to lead 100 tanks, APCs, and troop carriers.
The Last Stand of Gordon and Shughart. Outnumbered, knowing they have no hope of rescue, they insert into the crash site, move Durant to a building, and return to the chopper to make their last stand to try and draw the mob away from him. They know they're going to die, are explicitly told by a commanding officer that no support will be forthcoming (he won't let them go in unless they acknowledge this), but they're going in anyway. Those are the kinds of things that earn Medals of Honor, and Gordan and Shughart were both awarded the Medal posthumously in real life. Also is kind of a Tear Jerker.