Innumerable Left 4 Dead examples come to mind, but personal fav has to be a game of Versus on Dark Carnival stage 2. Other team had gone first and had managed to get everyone to the safe room, while in fairly good shape. Our turn comes around and we start getting hammered from the outset and it looks like we're going to TPKO sooner rather than later. Somehow we keep going, manage to get through the crescendo, but I'm the only one left standing. Rather than be a dick and run for the saferoom, I help two of the team up, then get incapped as one the others helps the last one up. My mate and the other guy limp off to the safe room, guy i revived helps me up and we all made it to the safe room, albeit with, like 10 health between us.
We lost the round 'cos the other team took less damage, but damn did I ever feel epic after that