UPDATED: In a 5-4 decision today, the US Supreme Court in McCreary County v. ACLU of Kentucky held that the Kentucky display of the Ten Commandments in two court houses violates the Establishment Clause, according to a report by CNN. Justice Souter's opinion for the court said that the predominant purpose of these displays was the advancement of religion. Though he said that in other contexts, like the frieze in the US Supreme Court, a neutral display that honors the nation's legal history would be permissible. Justice O'Connor wrote a concurring opinion. Justice Scalia wrote the dissent. The full opinions are available online.
However, also in a 5-4 decision, the Court upheld the display of the Ten Commandments on the lawn of the Texas state capitol in Van Orden v. Perry. Chief Justice Rehnquist wrote the majority opinion. Here is the full text of the various opinions in the case.
As an aside, I predicted this result (albeit cautiously) in an earlier posting.
(Also thanks to SCOTUS Blog for some of these leads.)