The circumstances of his death  received extensive coverage  both in Russia  (RUS) and abroad  (ENG). Letters and appeals he wrote from prison were published as well (an English translation  of one letter – at RFE/RL; scanned Russian-language originals of typed and handwritten documents  – at NewTimes.ru). The Public Oversight Commission for Human Rights Observance in Moscow Detention Centers issued a review  of the conditions of Magnitsky's prison stay (in Russian  and in English  – at Law and Order in Russia blog).
Due to publicity, the Russian authorities reacted by firing a number of high-ranking officials  – as well as by banning pre-trial detention of suspected tax offenders and drafting “a bill that would prevent executives from being arrested for the majority of economic crimes” (link to an article in the Moscow Times , ENG).
Public discussion of prison conditions, prompted by Magnitsky's death, continues – and it is now likely to move to a new level: Mikhail Ugarov (LJ user m_u), a playwright and artistic director of Teatr.doc  (RUS), a Moscow theater specializing in documentary drama , is working on a play that would “reconstruct” the horror of the final hours of Magnitsky's life.
Here is what Ugarov wrote  (RUS) on his blog on Jan. 22:
Working on a play at Teatr.doc about the death of Sergei Magnitsky.
[Russian actor] Aleksey Devotchenko will act in it.
Gathering of material is underway. Such material that it is making me physically ill.
Magnitsky died in a straitjacket. He was writhing in pain (pancreatitis or even pancreonecrosis), and they put a straitjacket on him instead. And he spent one hour and 18 minutes in it. And the doctor never showed up.
He died of “heart failure.” I think that his heart just stopped.
If the actor does a simple physical reconstruction of these events (the protocol of physical activity), the audience will get sick…
After all this, I don't want anything, don't want to think, don't want to feel.
And at serious theaters, let them go on re-enacting how Konstantin Gavrilovich shot himself [Konstantin Gavrilovich Treplyov, a character in Anton Chekhov's The Seagull ].
And here is an update  (RUS), posted by Ugarov on Feb. 2:
Yesterday again we had a meeting about the case of lawyer Magnitsky's death.
Things aren't exactly the way I described them – everything is more horrible, actually.
He told the prison doctor, “They want to kill me.” And on the basis of this, she diagnosed him as mentally deranged. And summoned the so-called “re-enforcement” – eight prison guards used to beating [prisoners]. And she called the psychiatrists.
And then she left, as if nothing happened. Her last name is known, this woman in a white gown, “Doctor Death.”
A ambulance crew arrived (the so-called psychiatrists), but for an hour and 18 minutes they could not gain access to the patient. And when they were allowed in at last, they saw a dead man. Then the doctor came down, too, to have a look… Paramedic Vasya (not his real name) stood in the hallway for this hour and 18 minutes and has no idea what this “re-enforcement” brigade was doing to a sick person…