I do think a set of good tools can help you grill like a master. While I'm a fan of specialized grilling tools that can handle specific tasks, like grilling baskets, a grilling lamp so you can see outdoors, or wide metal skewers (in the interest of full disclosure, I do design and manufacture a line of grilling accessories), there are five basic tools I recommend:

• As Chris points out, a stiff-bristled, long-handled wire brush for cleaning the grill grate. (You should use this twice: once right before the food goes on, and again after the food comes off and you're done grilling. In both instances, the food should be hot.)
  
• A set of long-handled, spring loaded tongs with rolled-steel arms (so they won't buckle when you go to pick up a beer-can chicken).
  
• As Sara mentions, an instant-read meat thermometer, so you can check the internal temperature of a pork shoulder or brisket.
  
• A chimney starter (if you're a charcoal or wood griller)—a vertical metal tube or box used for lighting charcoal without lighter fluid. You place the charcoal (preferably pure lump charcoal) in the top portion, a lit crumpled newspaper or paraffin starter in the bottom. Thanks to the chimney's vertical shape, the coals will light efficiently and uniformly in 15 to 20 minutes.
  
• Finally, a good grill book. Chris's The Thrill of the Grill remains one of the most sauce-stained, dog-eared references in my library.