Janet York (Day 1)
Janet York was Kim Bauer's best friend in the first season, and after a series of horrific acts the writers perpetrated against this innocent teenage girl -- she was roofied, her arm was broken with a crowbar, she was shot up with heroin, and then she was hit by a car -- she was finally murdered in the hospital by some creep who was impersonating her dad. Janet wasn't a major character, but this was the show's first season, and killing her sent a message to the audience: 24 isn't bound by the rules of your average procedural. Innocent teenagers get murdered here, and from now on you can't assume anybody is safe just because network conventions would normally keep characters like Janet safe.

Ryan Chappelle (Day 3)
As we all know, the Presidents on 24 tend to negotiate with terrorists quite routinely, even if they are demanding the completely unjustified execution of the head of CTU, in this case, Ryan Chappelle. Jack offered Chappelle the option of shooting himself, but when he couldn't do it, Jack had to do what was completely unnecessary and shoot the poor bastard in the head. It was the kind of tough situation that only exists on this crazy ass show, but it sure was sad.

Edgar Stiles (Day 5)
When 24 is out of ideas for your character, they don't play around. Edgar was Chloe's sweet, lispy teddy bear sidekick who couldn't make it to the sealed off conference room in time to evade the nerve gas. He tragically died in front of Jack and Chloe (and Kim, but who cares about Kim?) and got the sorrowful silent count-out to commercial reserved for only the most beloved of fallen 24 characters. I'm misty just thinking about dear departed Deadgar, so moving on!

Tony Almeida (Day 5)
Before the writers arbitrarily decided Tony's death was a fakeout this season, Tony's death was a pretty big shock. He was an immensely popular character, and he died in Jack's arms after being injected with an overdose of torture juice, which is about as Shakespearian as this show gets. I can't remember specifically if he also got the silent count-out to commercial, but he must have because I remember needing a minute to get myself together after the blow of no more Tony.

Curtis Manning (Day 6)
Gah, my arch nemesis, Day 6! Jack shot his best bud Curtis in the neck because he freaked out on a terrorist Jack had turned. An anti-climactic way to dispose of a majorish character? Absolutely. But the few seconds of the tension-filled standoff were so intense I wanted to throw up, and Curtis's death was as brutal and unexpected as 24 deaths can be. But to make it even sadder, after Jack sat down and mourned for a grand total of about four seconds he had to get up and run off to save the world again. It's always an understatement to say it sucks to be Jack, but really -- it su-huuucks to be Jack.

Charles Logan (Day 6)
The 24 Wiki claims Renee Walker mentioned that he somehow survived the attack, but I don't remember that and besides -- he definitely flatlined, which by Brothers & Sisters rules counts as being dead even if it's temporary, so I'm counting it. Anyway, Martha Logan went crazy and stabbed him! In front of Aaron! Whom she was living in sin with! It was awesome! Because Charles Logan had it coming, and he didn't deserve to spend the rest of his days under house arrest at his luxurious farm. Martha deserved her revenge a thousand times over. This is arguable, but in my opinion it was the most satisfying kill of the season, and one of my favorites of the entire series.

Graem Bauer (Day 6)
Obviously, anyone who's crossed Jack is going to die, but it was shocking that it wasn't Jack who killed him; it was their father Phillip, who was revealed to be a baddie when he killed his own son to prevent him from talking. While it's lame that everyone related to Jack dramatically turned out to be evil for some reason, that moment was a shocking turn. Until the plotline became completely ridiculous in the subsequent episodes, of course.

Dishonorable mentions:

Teri Bauer (Day 1)
It was nice to finally know that Nina was the mole, but honestly -- who didn't see Teri's death coming a mile away for the entire season?

George Mason (Day 2)
He had radiation poisoning and was going to die anyway; we'd all made peace with that. I will give him major points for choosing to go out in a huge explosion instead, however.

Jack Bauer (Day 2)
Because right -- Jack's just not going to be on the show anymore? Didn't buy it for a second, and neither did you.

David Palmer (Day 5)
It was sad, but it wasn't particularly shocking. He wasn't even President anymore when he was assassinated, and when you finally kill a character after five seasons of threatening to do so, the element of surprise gets a bit lost.

On a related note, how amazing is it that Aaron Pierce has survived seven seasons? If they ever do kill him I'm probably going to need grief counseling. Anyway, leave your favorite 24 deaths in the comments!