Tell Me (covered before here) has entered the free directory assistance market. The service says that it can find the phone number of any business in America for free.
Call 1-800-555-TELL (8355) and say "Business Search". You can then say the name of a particular business that you're looking for, or say the type of business that you want — such as "pizza" — to find options in your geographic area. You can optionally have Tell Me send you the company's phone number and address via text message.