Must have grilling cookbooks?
Chris Schlesinger's Thrill of the Grill is very good if you like his style of food which is pretty bold and uses lots of mangos for the salsas and sauces. Looks like the hardcover is out of print, but softcovers are available at ecookbooks.
I have used a couple of books straight from Weber.
Weber's Way To Grill.
Weber's Time To Grill.
Both books are good, and covers everything from setting up a grill to cooking or smoking somewhat complex recipes. Lots of good pictures too.