There are dozens, perhaps hundreds, of really cool grilling accessories, but you really need only three.
1.A long-handled stiff wire brush for cleaning the grill grate
2.Long-handled, spring-loaded tongs for oiling the grate and turning food
3.An instant-read meat thermometer for checking meat for doneness
That said, here are the near essentials and the not-so-essential-but-usefuls. A couple of good mail-order sources for grilling accessories:
www.barbecue-store.com (it also sells spare parts for gas grills)