isn't the most glamorous of Google's services, but the ability to call and get Google's directory service for free is indispensable if you don't have a phone with a browser. The service seems to be getting better all the time, and the latest feature will tell you the cross streets of the business you're looking for. That's a useful service in areas where building numbers are scarce, or all the roads have names instead of numbers.
To use this new feature, do a Goog-411 search like normal, giving your city or ZIP and saying your search terms. When the list of business comes up, and you choose one, say "details." It's not exactly a revolution, but it's the kind of basic, useful feature you'd assume Goog-411 would have had since the beginning.