This is a big topic for me, as I have about 60+ cookbooks at home. :)
One favorite is Aaron Sanchez' "Simple Food, Big Flavor" Each chapter starts with a new sauce, then he gives recipes that uses that sauce. I also like Rick Bayless' "Everyday Mexican"
I also use all three of Guy Fieri's "Diner's, Drive-ins and Dives" books. These books feature recipes from all the places he's visited and there are a ton of good recipes in them. Please note, these aren't Guy's recipes, they are the respective Diner's.
And one that you wont believe is really great is "Mario Batali's "Mario Tailgates, NASCAR Style" Don't let the title put you off, there is a ton a great stuff to cook, and I've never once tailgated, nor been at a NASCAR race. :)