I have three.
Maestro of the Black Dagger II, a multiclass halfling rogue/sorceror from Dungeons & Dragons v3.5. A cunning little bugger with a taste for treasure. Maestro was never the most powerful character stats-wise, but for some reason he was the character that always ended up bailing the rest of the party out of trouble.
I ran him in several campaigns. Not once did he die. Came close several times, but always survived in the end, and often was the reason that the party was able to beat the Big Bad. He wasn't powerful, but he was resourceful. Then our GM decided to run an epic-level game with no limitations on power. You could do anything for character creation. We ended up with a party consisting of a paragon illithid, a cyborg minotaur, a cleric whose level was so high that he was practically a demigod, a dire werebear fighter with a Constitution of 60... and Maestro. He was the only character in the party without a stat over 25.
And, of course, he was the only one who went through the entire campaign without dying.
Eventually, the Big Bad got wind of Maestro's exploits and designed a dungeon specifically to kill him. Our GM dubbed it the "Meat Grinder". Essentially, it was a three-mile-long corridor with every space being another epic-level trap. Oh, and the corridor was flooding with lava from one end. And the door on the other end was closing slowly.
Maestro made it out. The rest died.
Another is Brother Aloysius Regier, from a HackMaster campaign that I played in a while back. A Lawful Neutral cleric of a god devoted entirely to Law, his character concept was that he flipped the usual alignment axis. He ignored good and evil in favor of law and chaos. This caused quite a bit of party conflict, seeing as the rest of the group consisted of two thieves, a barbarian priest of a blood god, and only a single other lawful character.
Despite the fact that there was quite a bit of party conflict involved, everyone playing was a sufficiently skilled roleplayer to keep it realistic without disrupting the flow of the campaign. In my opinion, the best part of the campaign was when the barbarian priest burned down a temple to a local god (which rightfully belonged to a man living in the nearby village) as a sacrifice to his god, and Aloysius confronted him with a threat to throw him in jail. That was a great session.
And the final character is Jeremy Salter, a.k.a. "Daytripper". He was a time-manipulating superhero from a one-shot session that a friend of mine ran. He could only move back and forth on his personal timeline, and not exactly at will, but the power was entertaining and powerful without being broken, and the character ended up having a lot of attitude. I liked him.
"Sometimes it is better to light a flamethrower than to curse the darkness."
- Terry Pratchett