I am often asked to recommend an Excel book. This isn’t always easy, as different people need different things from a book, depending not only on their Excel ability and aspirations, but also their personality and learning preferences.
One consistent recommendation I do give, though, is for John Walkenbach’s Excel Bibles:
Excel 2010 Bible – John Walkenbach – Amazon UK
If you only want to get ONE Excel book, this would be it. There’s a bible for each version of Excel, and they’re an excellent mix of how-to guides, background information and reference material.