The Excel 2010 Workbook for Dummies is worth every penny. I taught myself the basics of Excel by following online video tutorials in conjunction with a couple of textbooks, but wasn't convinced that I was taking it all in. By working my way through the exercises in this book, which starts with the basics and progresses to Excel's advanced features at a logical pace, I reinforced the knowledge I had acquired.
As another reviewer remarked, it is essential that you have the CD containing the exercises together with video-based explanations. The book is only suitable for download if Wiley (the publishers) make those exercises available online.