the first two are from the U.S. Patent Office web site:
Trademark: A trademark includes any word, name, symbol, or device, or any combination, used, or intended to be used, in commerce to identify and distinguish the goods of one manufacturer or seller from goods manufactured or sold by others, and to indicate the source of the goods. In short, a trademark is a brand name.
Service Mark: A service mark is any word, name, symbol, device, or any combination, used, or intended to be used, in commerce, to identify and distinguish the services of one provider from services provided by others, and to indicate the source of the services.
Registered Brand: (took a bit of searching) this appears to be a registered trademark for a brand-name product. example: Xerox.
here's a web site that discusses all three: http://www.retailmerchandising.net/cbus/0400pti.asp