Numerical Mathematics and Computing, Cheney & Kincaid (the basics of numerical methods, a refresher course )
Computational Physics: Problem Solving with Computers, Rubin H. Landau, Manuel J. Páez and Cristian C. Bordeianu (an intro text with lots of examples worked out in detail. Scientific computing focused on the problem, rather than method )
Numerical Recipes in C (or C++), W. H. Press, et al. (The bible
of scientific computing for those who approach the subject from the application perspective, i.e. physicists, chemists, etc. )
The beginner's guide to Mathematica, J. Glynn et al. (A really good, albeit somewhat dated, intro into Mathematica. Lots of cool, easy to follow and non-trivial examples ).
Introduction to UNIX, D. Schwartz . (A nice thin book with lots of detailed examples. Perfect for those not on first name basis with UNIX )