NAMP Meat Buyer's Guide - Use what the pros use. This thick guide, produced by the North American Meat Processors, sounds expensive at $70 but you'll be amazed by the detail. Chock full of photos showing every possible cut of just about every commercially available animal. Highly recommended.
In-N-Out Beanie - Hit the slopes this year with some West Coast burger pride! This hat is awesome.
Lodge Reversible Griddle - This is the larger size (20") that will comfortably span two burners on your stovetop. Make burgers on a cast iron flattop, at home, without the sides of your cast iron skillet getting in the way.
Roll-A-Grill Bun Butterer - I own one (yes I do) and it comes in handy during burger parties when you have to butter 10 buns a minute.
Of course there is also the book which makes a fine gift as well as the photography from the book. And there's always the solid standby - gift cards from Five Guys, In-N-Out, and Shake Shack.