I have a whole list:
Telrav (Lures people to Nilheim, where his bandit buddies will slaughter you and take your stuff)
Alain Dufont (Arrogant bastard stole a family warhammer and basically shamed an entire family with it)
Hemming Black-Briar (Sadly, he's essential. He's also a complete waste of human life. Also might be an idiot considering the fact that despite saving all of Skyrim, he still thinks your skills in combat are lackluster)
Jaree-Ra (Had the audacity to get angry at you for killing her sister and all the Blackblood Marauders when HE'S the one who tried to have you killed)
Atar (Racist Nord who tried to oust Ainethach from the silver mine in Karthwasten. Murdered him even after intimidating him into leaving)
Thonar Silver-Blood (If you did the quest "The Forsworn Conspiracy" you'll know that he basically turned Madanach into his political weapon)
Grelod (If you talk to one of the kids before killing her, I think Runa Fair-Shield, she'll tell you about the room with shackles in it but in a way that sounds like she got molested....)
Commander Maro (Bastard basically ensured his own death by revenge-killing the entire Family)
Calixto Corrirum (Creepy serial killer who tried to resurrect his sister. You'll find proof of this in his journal if you take his key and use it to open his unpickable chest in his little museum in a shelf space directly above the doorway where you walk in)
Mercer Frey (This disgrace stole from the Thieves' Guild, murdered the last Guild Master, and tried to kill you. Truly, the shadows did take you)
Malyn Veran (Insane wizard who achieved a limited form of immortality. Soul trapped him for the irony)
Ancano (Power-hungry arse that tried to become a god through the use of the Eye of Magnus. Killed Aren and Ervine)
Sild the Warlock (Sadistic wizard. Likes trapping you in a cage and then burning you to death. Give him no mercy)
Naris the Wicked (Same as above, but at least he isn't as stupid as to try and kill you)
Mogrul (Words cannot even describe how much I hate this c*nt. At least he's smart enough to back off if you sucessfully intimidate him but I prefer murder anyway)
the Silver Hand in general ("He who fights monsters should see to it that he himself does not become a monster)
the Imperial Captain who tried to have you executed without a good reason (...bitch)
the adventurer who taunts you (the idiocy of their belligerent statements is... jarring)
those three "Soldiers" who basically ask you hand over 100 gold (They should be happy all I did was kill them)
the leader of Faldar's Tooth ("So you're the one who's been killing all my dogs? You'll pay for that!". Well, if you mean all the bandits I killed, then yeah I did)
Vampires in general are the most satisfying kills ("The only blood you'll be tasting is your own, nightspawn"). Thalmor and general warlocks come close
For me there are but three npc's that I would really put to the sword.
Hmm, Maven Black-briar. At the source she is all that is wrong in riften, without her support the Thieves Guild would have been massacred a long time ago.
The next one would be Astrid, because well... she betrayed the whole family just so she could get to me.
And last but not least Delphine. I don't care for Paarthurnax to live or die, however I find it most frustrating that she, a member of the blades, has the audacity to order you around while you are the Dragonborn, the guy they are supposed to serve.
However, as far as my most satisfying kills until now are numerous, but I'll give the two most important,
The Emperor, both times, I loved the way he faced his imminent death, with dignity and honor, not with fear and cowardice like I had expected, in fact this completely changed my opinion on him, he never signed the treaty out of fear, he did in fact do it out of dignity, he admitted his loss so none would be killed after, whether that be necessary or not. Also the excitement of watching his double eat the meal you prepared.
And the guy who asked you to kill the emporer, this was for a ore personal reason: When I first played through Oblivion, I joined the dark brotherhood and loved it, until I had to break into the Motierre residence. I had no real clue how to lockpick (remember we are dealing with a raging bloody twelve year old who still skipped through tutorial Windows) and let's just say the odds were not in my favor when autolockpicking and that led me to use over 400 sodding lockpicks to get into the house of my contractor... Let's just say killing the great Grandson of said contractor felt like the nicest kill ever, vengeance at last.
Well for me Ancano deserves a torturing death not because he seeks immense power,not because he kills Aren and Mirabelle but because he sends that damn Thalmor right after dealing with the Dragon Priest inside Labyrinthian. I was cocky enough not to save aftet the fight and got punished really hard when he owned me because I was cought off guard. The second time I left a disintegrated pile of ash inside that ruin. However not Ancano,not Nazim with his cloud district or even that good for nothing high elf in Solitude who would even degrade Ysgramor for what he was wearing even come close to how much I'd like to transfrom in a Werewolf and bite Maven Black-Briar's head off. I despise the thieve's guild,Riften and every single associate this evil woman has just because of her. Unfortunately I play on a PS3 and can't use a mod to lift the immortality
And of course, who could forget the Thalmor? I make it a point to visit the Thalmor Embassy whenever I can to "clean house" and leave one alive to send a message to the rest of the Dominion that us Nords are not to be trifled with. I also make it a point to hunt down any Thalmor I see wandering the wilds of Skyrim and leave them for the wolves to find ;P
Here is my list:
Elenwen - She is the one who ordered the justiciars to kill the adoptive Nord parents of my Thalmor Slayer Khajiit. I just enjoyed to see her scream like a witch when I soultrapped her.
Arcano - The king bitch of Mundus learned the hardest way that one who is lust for power fails to see the tragic ending. Like Elenwen, I soutrapped him.
Molag-Balls and Boethiah - After forcing me to kill a vigilant of Stendarr, Molag-Balls had the guts to order me to lure a priest of Boethiah to him. I simply soutrapped Logrolf and sent him to the Ideal Masters as a way to say I serve no daedra. And I even pissed off Boethiah in the process
Delphine - I made a discussion about her so I won't repeat again.
Thalmor in general - They claim themselves to be the superior race so I make enchanted items with their superior souls so that I don't need to level up Enchanting to 100.
Grelod - I soutrapped her and made an enchanted wood sword with her soul and gave it to Runa Fair-Shield. Sweet revenge
Black-Briars - Sadly they are essencial, so I do everything to sabotage their operation such as smuggling a Black-Briar keg to Ivarstead, steal Frost, lie to Sibbi about Lynly, destroy the Dark Brotherhood and don't join the Thieves Guild.
Cicero - The keeper is a sacred position in the Dark Brotherhood, but it is performed by the wrong man with wrong behavior and wearing a wrong outfit. Needles to say I hate the way he speaks.
Thonar Silver-Blood - Watching Madanach killing him and raising him as undead was such a sight
Telrav - I did different. I killed his men first and then I loved his reaction when he lured me to the trap and saw his friends dead.
Mogrul - In my wallet money don't go away, money come to it. So I killed him.
Yes it's true that with all the anomalies spawning and the mandatory use of Staff Of Magnus while Ancano channels power from the Eye it's more like a mini game than a real fight. Plus you can't kill him in any fancy way,just straight up kill him. You're lucky if you get a kill cam which I've never gotten. Not as fulfilling a fight as I excpected.
Ancano. That high elf is the most grating character in all of Skyrim. Nazeem and his Cloud District saying drives me mad. I frequent the Cloud District regularly, thank you very much. And finally, Britte, Sissel's sister. That's the one child in Skyrim that could use a Firestorm spell...
I also have an entire list of people I thouroughly enjoyed killing
Nazeem: One day I'm going to Fus Ro Dah him all the way to the cloud district, even if it's out of my character's roleplaying standards.
Thalmor justiciars: If you think the stormcloaks are racist, you obviously haven't met a Thalmor agent. They're basically Nazis, thus resulting in me killing them on sight.
Mercer Frey: Greedy imbicile thinks he can outsmart the Dragonborn, when he can't even sneak through a cave without battle taunting and waking up all of the undead.
Elenwen: Same reason as the justiciars.
Ondelmar: HIGH ELF SUPERMACY. Oh how I enjoy killing him.
Delphine: Oh how I wish I could kill her. However I'm a console peasant and can't use mods. Reason why I hate here is because she wants to boss the DRAGONBORN around, and make him her errand boy.
THE MOST SATISFYING KILL I HAVE EVER HAD! WHERE DO I BEGIN!!!!
I have to give it to when I killed Elenwyn with Kavohzein's Fang enchanted with Absorb Health+Fiery Soul Trap (Fire Enchanter and Augmented Flames 2/2.) and the Wabbajack! I stole her soul and turned her into a pile of Septims and residue....
Heres my list. Ancano with his superior ways and plummy tones, that little brat of a child from whiterun who is always cheeky and gobbing off, Maven black briar (without her the thieves guild wouldn't do so well, and lastly for the moment that brynoff who recruits you for the thieves guild how dare he make such a statement "never done an honest days work in your life lad for all that coin you carry" cheeky t/.;'.