That "I, Claudius" DVD edition I mentioned a while back? So worth it. Among the extras are interviews with cast and crew, an extra documentary where they name their favourite scenes, and, available nowhwere else, "The Epic Which Never Was", aka a legendary black and white documentary on the movie "I, Claudius" which Josef von Sternberg was supposed to shoot, with Charles Laughton as Claudius, Flora Robson as Livia, Emlyn Williams as Caligula and Merle Oberon as Messalina. Several weeks into the shooting Merle Oberon had an accident, and since her husband, Alexander Korda, was producing, there was no way they'd replace her. Which meant that was that.
(The TV cast of "I, Claudius" jokingly refers to the Claudius curse, similar to the Scottish Play curse apparantly, when recounting their own misfortunes.)
Fortunately, some rushes of the planned epic movie survived. The documentary presents them in a fascinating way. First we see them as ordinary rushes, i.e. we see and hear people yelling "cut", and the actors dropping out of posture once it's done. Then, later we see the various rushes cut together as a movie scene would be, and your heart bleeds for what could have been. There is von Sternberg (aka He Who Discovered Marlene Dietrich And Never Let Her Forget It) with his inimitable lightning, sculpting actors' faces like no one else. And with his taste for sadism; the humiliations Emil Jannings goes through as Professor Unrat in The Blue Angel has nothing on Claudius being humiliated by the entirety of Rome.
And then there's Charles Laughton as Claudius. Who is different and similar to Derek Jacobi as Claudius; it's like seeing two great takes on a Shakespearean part like Richard III by two very different actors. The scene in which he goes from ridiculed bumpkin Claudius to Claudius the Emperor taking control of the Senate is breathtaking, like a butterfly out of a cocoon.
(In the TV series, a quite different scene has a similar impact - when Livia has invited Claudius to dinner, and he, not knowing whether she's going to poison him or not, drops the fool's exterior and really talks with her without a mask for the first time in his life.)
Emlyn Williams as Caligula is quite similar to John Hurt's performance in the TV series, except I think Hurt's Caligula comes across as even more dangerous due to being more intelligent in his madness. But it would have been the performance of Williams' career, no question about it; I wonder whether they'd have managed to get all that bisexual innuendo past censorship then.
This documentary also features an interview with Robert Graves; it was the first time I saw and heard him. The light, crisp upper class voice sounded quite different from what I had imagined - for some reason, I figured Graves would have been a bariton. Odd to think Graves was still alive at the time that particular documentary was made when one associates him so strongly with WW I. and the immediate aftermath.

As for the scenes in "I, Claudius" the TV series which were selected as favourites by the cast and director/producer Herbert Wise (scriptwriter Jack Pullman, alas, succumbed to the Claudius curse and died), here are some examples :
Brian Blessed (Augustus): The "did you sleep with my daughter?" scene in which Augustus has assembled the various senators who did just this. His other favourite scene was also one of Wise's: the death of Augustus. Which is one amazing thing but I'll come to that. First, though, about Blessed: he's one endearing fanboy in those interviews, insisting that this was the best TV show ever, so there! His Augustus was amazingly low-key considering Blessed (aka Prince Vultan of Flash Gordon fame, aka various shouting villains in lots of British genre shows from Blake's 7 to Dr. Who, but also the Ghost in Kenneth Branagh's Hamlet) is otherwise known for BEING EVER SO LOUD.
Herbert Wise (director/producer): Augustus' death scene, as I said. He's justifiably proud of the approach he took. We hear Livia talking all the time - and it's a crucial, revealing monologue - but the camera never moves away from Augustus' face, for about four or five minutes. We do see the light going out in his eyes, as Wise puts it - this is where Brian Blessed delivers his best acting ever - and still the camera doesn't move away but shows dead Augustus for three more minutes, until finally Livia's hand moves in to close his eyes.
It didn't surprise me Wise picked this scene, but his other pick was a surprise (not because the scene isn't good but because it's not one which immediately comes to mind): it's a scene between Claudius and Sejanus (played by Patrick Stewart), in which, to quote Wise, Claudius enters a room through one door being married to one woman and leaves the room three minutes later through another door married to another woman. (Because Sejanus tells him he's supposed to divorce his wife and marry Sejanus' sister instead.) All, says a proud Wise, in one take because he could rely on Jacobi and Stewart as actors. "I, Claudius", he continues, is in many ways a horror comedy, and the comedy part is crucial. (Being the BTVS fan I am, I wondered at that point whether Joss during his English years had watched the series.)
John Hurt (Caligula): The scene in which Caligula tells Livia he won't make her a goddess after her death. Both Hurt and Wise say it was Hurt's idea that Caligula would get into bed with the dying, helpless Livia to tell her this. Wise wasn't sure whether they could get this past the censors ("at that time, people were rarely shown in bed with their wives let alone their great grandmothers") but Hurt insisted, and so they shot it this way. It's Caligula at his sadistic and perverse worst, with nothing more than some whispers and a kiss, and though Livia was a fearsome presence up to this point, you can't help but feel sorry for her. (She keeps her dignity, too. A single tear but otherwise she doesn't give him the satisfaction of a reaction.)

Oh yeah, and everyone's pick for most gruesome scene: one of these examples of how insinuation works much better than actual showing, because you don't really see anything. A door opens, that's all, basically. Recently, in London, Kathy told me she never could rewatch it, and I empathize. Here's how it works: Caligula has gotten it into his head that the child his sister and lover Drusilla is pregnant with will be more powerful than he is (a la Kronos, Zeus, etc.). We see him tie her up and she thinks it's one of their games. Next thing you know, Claudius, knocking on the door, finally gets Caligula to open it. Caligula, still in Zeus masquarade, has blood on his mouth. And then we get a reaction shot from Claudius to what he sees beyond Caligula in the room.
I had nightmares for a week.

Aside for Babylon 5 fans: The Emperor Cartagia was very obviously modelled on Caligula as played by John Hurst in "I, Claudius", and all the Centauri Prime scenes are distinctly influenced by this show. One can argue whether Vir or Londo is Claudius. Of course, one of the most chilling moments during Cartagia's reign is the simple closing of a door (behind which we know G'kar to lose his eye).

In other news: for a love declarations to several characters (Buffy, Xander, Angel, Connor, Wesley, Harry Potter and Draco Malfoy) which awakes my inner cheer leader (welll, except for the Draco bit, but she puts it in a way which at least makes one understand the motivation) , read this.