From Tom Mighell at Inter Alia:
Have you checked out AltLaw yet? It's a search engine that will let you search the full text of U.S. Supreme Court and Circuit Appeals Court opinions. The current coverage from these courts is so far not great, but still pretty impressive: Supreme Court opinions from May 1991, and circuit court opinions from various dates (the earliest 1992), depending on the court. Currently there are more than 184,000 cases in the database.
The search function is pretty easy to use -- just enter your terms, and the results allow you to view an HTML preview of the opinion. You can then download the original opinion in PDF, or get a text-only version.
AltLaw is a joint project of Columbia and University of Colorado Law Schools. It has a long way to go, but as a free search tool for case law, it's a promising start.