Sharpie Sketches - Horses by ColossalBeltloop . I once heard an artist say that she liked to draw in pen because there was no erasing, and it helped her learn to accept imperfections. That seems like a good (albeit somewhat painful ) idea!
If you love animals or drawing then you should add this book to your collection. The Art of Animal Drawing is a crash course in not only animal anatomy, but usage of lines, page composition, animation.