Western leaders to have been prosecuted for torture/human rights violations.

[Stranger in a strange land]

Pinochet died under house arrest. A very mild punishment considering what he did, but still, it's at least something. Do you consider Pinochet a Western leader?

[Stranger in a strange land]

Also, not sure if he counts, but P.W. Botha was tried and convicted for refusing to appear before the Truth and Reconciliation Commission to answer for his role in the bombing of the South African Council of Churches. However, he successfully appealed his conviction.

Also, obviously Nicolae Ceausescu. However, from what I've been able to gather, none of the other Communist East European leaders faced any punishment after the collapse of Communism, aside from Zhivkov, who was placed under house arrest for embezzling funds.

[Stranger in a strange land]

I'm tempted to throw Eichmann into the mix here.

Does he even count as a leader?

even if he does, we've pretty conclusively established in this thread that Botha, Videla, Pinochet, and the members of the Greek Junta have all been prosecuted much more recently.