Justice Antonin Scalia said something interesting in an interview on 60 Minutes on Sunday.
Excessive bail shall not be required, nor excessive fines imposed, nor cruel and unusual punishments inflicted.
Apparently Scalia believes that when the US government tortures prisoners at Guantanamo Bay, it's not a violation of the Eighth Amendment, not because torture isn't cruel and unusual, but because it's not punishment. They're not being tortured as punishment for their crimes, they're being tortured to extract information, that's a completely different situation.
It's an argument I've never heard before, but Scalia's got a point. The Eighth Amendment is clearly talking about punishment for crimes as sentenced by a court, but the prisoners at Guantanamo Bay have never been convicted (or indeed charged, in most cases - so the Sixth Amendment is still out the window). So while torturing prisoners still obviously violates the Geneva Convention Against Torture, it doesn't appear to violate the Bill of Rights.