We only started Savage Tide last semester, so I know this obituary is kinda late, but it's still pretty impressive.
Cole Greenshoals, aquatic halfling scout: not technically dead, but in the care of the church of Kord after succumbing to the savage tide from a pirate in the first adventure.
Dagalur, orc fighter/ranger leviathan hunter: killed by the aquatic hydra in a massive underwater battle. Pretty straight-forward, but it definitely ranks as the most character appropriate death.
Graath, hadozee rogue: death by the cobalt dragon I placed on an island at the end of the Pearl Current to give PC's more XP. I believe it was death by all-out assault after several breath weapon attacks had failed.
Eric, human hexblade: a pretty straight forward stand and deliver death at the hands of the Mother of All, I let his soul be taken up by Procampus since his death pretty much gave the other PC's the chance they needed to kill that b***h of an abberation.
Kjell, human fighter (Dagalur's replacement character): death by tyrannosaurus, along with Skald, who had just started to be liked by the PC's. This still rates the most vicious encounter of the game so far; I mean, seriously, you wake up from being shipwrecked then BAM!!!-tyrannosaur.
Darrin, human dusklblade: failed a will save vs. mummy fear in the Olman catacombs, followed by two simultaneous mummy criticals resulting in 43 points of bludgeoning damage to a skull. (This was Eric's replacement character.)
Lukin Greenshoals, aquatic halfling rogue/scout: In 25 years of playing D&D, this was the first player character I've had die from mummy rot (after 6 days-a pretty gruesome, cool, yet realistic death by disease.) Mummies 2, PC's 2-the third mummy was just bull-rushed off one of the narrow stone bridges, waiting for all eternity for his chance for revenge.