That's obviously a massively wide field - any particular business topic that you're interested in? Given we're on HN, the VC world is often of interest - I can recommend Brad Feld's 'Venture Deals' if you want to get an easy to digest "anatomy of a venture deal" book. If you want something more geeky on the finance side, you'd be hard-pressed to overlook the Allen & Brealey bible 'Principles of Corporate Finance.'