If you’re starting out piano, there are many good book choices. For younger beginners I recommend Me And My Piano, they go quite slowly adding one note at a time and give each new note a new colour. For older children and adults, the Piano Time books are very useful, they take you through everything faster than Me And My Piano. I’ve also heard good things about the First Piano Adventure book, but I’ve not used it myself.
The amazon links are below:
Me And My Piano
http://www.amazon.co.uk/dp/0571532004
Piano Time
http://www.amazon.co.uk/dp/0193727846