Knotted Doughnuts and Other Mathematical Entertainments
Martin Gardner
W.H. Freeman & Company
I loved reading Martin Gardner's books since I was a kid.  Unfortunately, though packed with mathematical curiousities, I found the present book a drag to read.  Some chapters were particularly dry and others just too mechanical.  The addenda to each chapter, trying to beat each topic to death, detract from the flow of the book.  There are some nice problems in there, but you may want to skip some sections altogether.