I had a lv5 paladin lv1 hunter of the dead on a ship which got ambushed by some lizard men, a sea hag and a sea ogre, the sea hag was dispatched with little effort (I had some great rolls), then I set about the sea ogre which started bad and I got some attacks in but did little damage(I rolled 1's for my damage), we then went several rounds missing each other, which raged the ogre and eventually he hit me and did something like 63 points of damage which sent her body in one direction and her limbs in another, we was on a quest which involved a chalice which was in my backpack which was on my back when my torso sailed into the sea.

3.5e.
My human fighter (I think it was a fighter) was in a dungeon with a group of others, and he was the only one without darkvision and didn't have a torch either. So we were fighting this group of enemies in a very large hall, where my character was trying to retreat from battle after being wounded. He retreated.... directly into a huge, gaping pit, where he failed his reflex save to grab on to the ledge. His final, immortal words were "I regret nothing."

I was dming a PbP for the first time. The adventurers began on a river boat, on its way to another town. In order to get the group together, I think "why not a good encounter to start with?" I choose a shapeshifting aquatic monster: it appears like a woman drowning. The druid decides he'll try to save her, and so falls in the trap: the monster grapples him and attempts to drown him. The druid decides he won't fight, so he'll keep his breath longer. Nice idea, but the rest of the group just watch him sinking, without doing anything...
Most annoying death ever.

Another one. I was playing an 8th level barbarian, using a +1 Guisarme. Our group come accross a Tyranosaur Rex. A fiendish Tyranosaur Rex. My barbarian doesn't bother and charges the thing, but the T-Rex has more reach and on its AoO, it bites and grabs the barbarian. Two turns later, T-Rex swallows the barbarian. I have a back-up dagger, but its not magical, so it's very hard to dig a hole in the gizzard (the fiendish T-Rex had damage reduction/magic). So while fighting for his life, the rest of the party continue to fight it. And the last damages were done by my barbarian finally cutting through its gizzard, down with 2 or 3 HP out of 82... Pretty funny death for the Fiendish T-Rex!