The hardest encounter I have had was when I was fighting an ancient dragon, got him down to 3/4th of his health bar... after he flew off and I went after where I saw a dragon come down. with full health... it was also an Elder Dragon :(. I had to fight both dragons at the same time! Both doing frost breath attacks and bite attacks ><.
The funniest encounter I have had is with Imperial guards marching a captured stormcloak... a wolf near by aggroed and the storm cloak ran a head and killed the wolf but instead of running off he just went back into the line as a captured stormcloak... he could have ran away... gone for freedon.
i had that happen!!!! the leader was an orc was yours?
Not sure about that poster, but I've had this 3 times on the same character, the leader was always a male orc and there was another male meleer with him and a female spell caster. The first time I had it, they spawned near a guy labeled "Mage Apprentice" or Novice or something. They'd always one shot kill him, seems two random encounters hit at the same time, after a few reloads I managed to save him using Ice Form and some luck. He only had a pathetic staff and no magical abilities of his own, he decided to give up on magic and handed me his staff of something... he never moved at all after this and was killed about 20 levels later by another random encounter when I went back past that area.