Book: Fortran 90/95 Explained, by Metcalf & Reid.
One of the greatest books available on the topic, written by two of the members of the committee responsible for the Fortran standardization process. Self-contained and comprehensive, this piece is a must-read for scientists who deal with programming, numerical methods and computer simulations on a daily basis.
If you find the book useful, please buy it. It is one of those books you will like to have on your shelf.