My Favourite Book: The Flavour Thesaurus
This book is pretty much the best book ever.
Next to my trusty (and crusty or 'well-loved' as some would say) Cook's Companion, this book is always a fantastic reference when I'm mucking around in the kitchen, for finding out what goes with what.
I could sit here all day talking about what flavours compliment one another and there's definitely a science to it, really it can be as simple as how tomato and basil work together or something as complex as the components on which most Asian dishes are built on; sweet, salty, spicy & sour. Ingedients that need to live harmoniously together in order to create the perfect balance of flavour.
But honestly, you're better off having something like this to reference so you can look up the specific ingredient you're using and try different combinations. It's definitely a must-have for any aspiring cook or chef!