To Westlaw and Lexis:
You have a big head start, but the world's largest search monster just left the land of nightmares and placed itself squarely in your rearview mirrors. Google has surfaced search functionality that will return full-text opinions from state and federal courts. Google Scholar, still in "beta," allows searches by case name, topic, or key words. Advanced filters allow for creative search construction. The November 17, 2009 announcement on Google's blog is here.
I did some test searches, and the results are good, but not quite as current as Westlaw or Lexis would provide. Each case, when viewed, includes a "how cited" tab that, rather than explaining the correct citation syntax, provides a list of other cases citing to that case and an interesting list of case quotes showing how the case is cited in context. Testing with Tobacco II, I was able to find that Cohen v. DirecTV cites Tobacco II, but Cohen isn't yet returned as a result when searching for it by name. Either Google is waiting for finality before providing access to opinions, or its data source is slow to update. As another plus, the cases include pagination information.
Setting all else aside, it's free and it's simple. At this point, Westlaw and Lexis should stock up on clean underwear.