A classic that I found valuable is Science of Programming David Gries, 1981 http://www.amazon.com/gp/product/0387964800 It is still in print as a paperback. Several ssed copies are $11 shipped to US - a bargain. Gries is a died-in-the-wool iterationist. His cursory discussion of recursion is not worth much, but he really knows iteration with while.