The interesting, useful and enlightening.

Here's some books that I've found useful. Just so you know, I get a cut if you choose to buy any of them via the links to Amazon.

Brand Portfolio Strategy by David A Aaker (a great guide to how you make sure all your brands interact effectively)

Contemporary Strategy Analysis by Robert M Grant (primer for strategic planning)

Dictionary of Quotations (inspiration!)

The Economist Style Guide (grammar empowers)

Lend Me Your Ears by Max Atkinson (how to make your presentations relevant and engaging)

Marketing as Strategy by Nirmalya Kumar (I was lucky enough to be taught by Nirmalya)

Marketing Judo by John Barnes & Richard Richardson (marketing on a budget)

The Non-Designer's Design Book by Robin Williams (making things look pretty)

Roget's Thesaurus (in case words fail)

Wally Olins On Brand (I was lucky enough to work with Wally whilst I was at Thomas Miller. This book is very inspirational)

We, Me, Them & It: How to Write Powerfully for Business by John Simmons (exactly what it says on the tin)