Whitfield v. United States, Supreme Court of the United States, Justice Sandra Day O'Connor, January 11, 2005 [ruling that a count of conspiracy to commit money laundering does not require proof of an overt act to further the conspiracy]. Excerpt:

As the Government points out, Congress has included an express overt-act requirement in at least 22 other current conspiracy statutes, clearly demonstrating that it knows how to impose such a requirement when it wishes to do so. See Brief for United States 11, and n. 5 (citing statutes). Where Congress has chosen not to do so, we will not override that choice based on vague and ambiguous signals from legislative history.

Read the full text of the opinion here. Reported in JURIST's Paper Chase here.