Deaths I have seen:
Keep on the Shadowfell, final battle. Our wizard falls, and is being sucked into the planar rift. We burn all sorts of action points, risk OAs, and do everything possible to drag him out just in time... for him to fail his last death save anyway.
Mid-paragon, while the group is trapped in some sort of ghost round, our bard drops in the midst of a tough fight. No other easy way to get healing to him, the one shot we get at stabilizing him fails, and he bleeds out during the fight.
Mid-epic, the party is infested with Chaos Phage (and made an agreement to not try and fight off the infection magically). Most fight it off naturally... the Avenger does not, and Slaadpoles burst from his forehead. Same happens with the Warlock, but he's a level 24 Lich, and so instantly puts himself back together again.
A few levels later, the party is trapped in ancient Nerath and fighting hordes of Gnolls. The Avenger goes toe to toe with their warleader, a ranger who unleashes a Blade Cascade. A few hits, and the Avenger hits negative bloodied - though the Warden, nearby, is a Guardian of the World Tree and can die in his place and then return the following round.
Later, while suffering another nasty affliction, they decide to use Remove Affliction on it despite it being a level 30 effect. They do this carefully, when they are pretty confident the Avenger (also a Deva) won't fail the check. After getting a good deal of success, he offers to cleanse the Warden (despite the Warden having been doing pretty well fighting it off naturally). Natural 1 on the heal check, and natural 1 on the Memories of a Thousand Lifetimes to boost the check, and the Warden dies.
There may be one or two others I am forgetting. Not a ton, but enough to keep the party on their toes - lethality has gone up a bit since reaching Epic (partly due to the fact the party has several 'return from death powers' anyway).