I think I’ll narrow 24 down to one major character for each of the first three seasons. Others died, but maybe aren’t really “major”:
1:
Jack’s wife
2:
George
3:
Ryan or Nina (arguments for both)
and for 4:
They faked us out with Tony.
Did Mandy die? I don’t remember her dying for some reason.
Also, jsgoddess -
Jack technically died in both seasons 2 and 4. 
Major character deaths on St. Elsewhere:
Dr. Daniel Auschlander (died of a heart attack, ironically after surviving six years w/ liver cancer).
Dr. Elliot Axelrod (obesity-related heart disease).
Dr. Peter White (shot in the nuts by nurse Shirley Daniels).
Dr. Wendy Armstrong (suicide - swallowed pills).
Mrs. Hufnagel (death resulting from surgical mishap, and negligent medical care).
the Birdman (suicide - jumped off the roof of the building).
Dr. Mark Craig Jr. (car accident - which also left his then-pregnant wife in a coma. The baby survived though.)
Nina Morrison (accidental death, hit her head - her heart was transplanted into —
Heart-transplant Woman (name I can’t recall - her body rejected the heart.)
And before anyone chime in that, technically, no-one died since this was all the imaginings of Westphall’s autistic son, let me remind you that on some metaphysical plane of reality, Buffy Summers is simply a catatonic delusional schizophrenic who thinks she is a super-powered Slayer of Vampires, and thus no one on Buffy and consequently Angel died either.
interface2x:
Hmm. I thought so, but I could be mistaken.
Ha! I guess you’re right, but I think that doesn’t qualify for the OP.
Remember, “only permanent deaths count.”
Shucks.
The death rate for paramedics on Third Watch was pretty high.
In the series premiere, Jerry got shot and nearly died. Then Bobby got shot and killed by his junkie friend, and later Alex was blown in two by a car explosion.
If you add in Doc’s breakdown after 9/11, the odds were not good for medics at the 55.
Well, if you include the last 15 minutes of the series finale, I’ve gotta say Six Feet Under.
There’s a musical montage bit where every single significant character of the series is shown as they die. Pretty much a 100% mortality rate for major characters.
And the Sopranos may not be in the lead, but it’s gotta be fairly high up on the list. Although, like the aforementioned Oz, the structure of who qualifies as a regular or recurring character is a little different than in regular network shows.
thwartme
I never watched it myself, but what about NYPD Blue? They seemed to burn through their characters pretty quickly.
ISTM that Faith meets rule (b) in Buffy. She appeared over the course of three seasons, and certainly more than ten total episodes.
Well, who said she didn’t??
She never dies though. Comas don’t count.
fabulous creature said that Faith wasn’t major in Angel… which is fair, since she was never a regular and…
(spoiler for Faith’s episode count on Angel… not sure if this is necessary but anyway…)
Two episodes in season 1. One episode in season 2. Three episodes in season 4. That’s only six angel episodes.
Technically, no-one died in any pre-90s series because roughly 90% of primetime TV was in that kids head!
Going back to ER, you’d also have to include Mark’s father (appeared in at least 10 episodes, and over two seasons).
Not sure if they meet the requirements are Mark’s mother (she was in just a couple of episodes) and the other med student who died; I can’t remember his name he either fell or jumped in front of an El train.
Here is what I came up with so far on Melrose Place, although I will have to dig up a full character list to see the fraction of total cast. All these characters were either opening credit regulars or recurring across 10 episodes/ 2 seasons.
Characters killed in accidents:
Kimberly (died twice! but came back once. I included her in accidents because her car accident was the initial cause)
Sydney (car accident, run over)
Alycia (car accident)
Brooke (drowned in the pool)
Hayley (drowned, fell off boat)
Characters killed by other regulars:
Mackenzie Hart (killed when Kimberly blew up the building)
Richard Hart (killed twice! once by Sydney, rose from the grave and then later shot by cop)
Reed Carter (shot by girlfriend Jo)
Jesse Hanson (fell off construction site in fight with Jake)
Jack Parezi (fell from stairs in fight with Amanda)
Bobby Parezi (pushed out window by Alicia)
Characters who killed themselves:
Bruce (Amanda’s boss)
Keith (Alison’s boyfriend)
Craig (Sydney’s fiance)
Oh, I’d definitely call Faith a major *Buffy * character. But since she survived both that series and (as far as we know) Angel, it doesn’t matter for this discussion.
I would certainly consider this one a major character:
Sherry Palmer
You’re right. I had her on my earlier list, then I thought I was being clever by whittling it down. I should have known. I’m never clever, dammit!
Linwood. If I may say so, one of the best deaths ever shown on Angel.
Decapitated by his own chair! “Great hints on office furniture” indeed!
I don’t know if it’s within the rules of the game but Gunn was said to have 10 minutes to live. So is he technically dead? If so, that means that all the humans who worked with Angel died in the course of their duties. So if Angel ever asks you to become a part of his detective agency… just say no!
I’m getting tired of typing these spoilers, but I just have to be polite…
Angel spoiler
I deliberately didn’t count Gunn, as well as Angel, Spike, & Illyria, because they were alive as of the last minute in the last scene. Yeah, I THINK they’re all dead, but it’s not impossible they survived. The Powers that Be might have sent reinforcements, or Faith & Willow might have appeared with a couple of dozen Slayerettes. (I think Faith was more likely to give Angel the benefit of the doubt than Buffy.) Unlikely, but not impossible–and since we don’t know that it didn’t happen, we can’t count them as definitely dead.
I nominate Blackadder.
At least one major fatality every season. Two seasons ended with (almost) the entire cast buying it. Not bad for a light comedy.