I know of two memorable "Last Stand" experiences, both in WoW. The first during a heroic Slave Pens group, we had pulled the giant crab (whose name escapes me at 6am) when all of a sudden our tank goes down. Right after the healer gets squished and both our melee dps, then it's my turn, I snap off a fireball (I was playing a mage)as the beast starts bearing down me, I start casting a second one, if I can get it off he'll die as he only has 1,000hp left. It came down to a race between him getting to me, and my cast bar. My fireball shot out just as he reared up to do his attack emote, smacking him for a 2k crit and laying him down. I think I actually may have yelled "That's how it's done, B***H!" into my mic.
The other instance of this, I wasn't the hero, in fact it was my dwarf pally tank who saved us. In the new instance, Halls of Reflection, we were on heroic, and the last 'boss fight' is actually just running as fast as you can before Arthas catches you in his little "I kill you now" aura. We has got slowed down at teh halfway mark, and we were cutting it right down to the wire, sometimes only making it through the barriers with inches to spare. At the last barrier, Arthas was bearing down, I remember looking down, my back was plastered to the barrier wall, and Arthas' aura was mere feet from giving me a bad case of frostbite, our tank types in chat "I got this" and leaps through the AoE at Arthas, who promptly stops, one-shots the dwarf so fast you can almost hear Arthas say "WTF?" But that one second delay was all we needed, we killed the last undead, broke down the barrier and made it out onto the balcony to be rescued by the Skybreaker, In party chat we then had a long discussion about how the tank knew that would work, to which he replied, "I didn't, we just didn't have any other options."