Here are some links to other open texts that I have some manner of affiliation with. (See the American Institute of Mathematics site for a good list of good open texts.)
APEX PreCalculus: A precalc book written by my colleague Amy Chapman, with Meagan Herald & Jessica Libertini. It matches the look of APEX Calculus and covers introductory material well. Available at Amazon.com for under $8. Source files are available on Github.
Active Calculus: A full calculus text written by Matt Boelkins with David Austin and Steve Shlicker, written in an "active learning" style. This is intentionally not a traditional calculus text. It is very well written with Geogebra and WeBWorK support. It is very popular; the .pdf's have 70,000+ downloads and a number of schools use it as their calc text. Available at Amazon.com for under $20; find out more at activecalculus.org.
Fundamentals of Matrix Algebra: A text I've written for students needing a background in matrix operations without most of the theory included with "Linear Algebra" courses. The text covers Gaussian Elimination, matrix algebra, determinants, eigenvalues/vectors and a few other topics. Available at Amazon.com for $10; download a pdf version here.
An Introduction to MATLAB and Mathcad: A text written by my colleague Troy Siemers that covers the basics of using MATLAB and Mathcad, along with basic programming principles/structures such as if/then, loops, etc. Available at Amazon.com for $8; download a pdf version here.
Essential Precalculus: Another precalculus book produced in the APEX Calculus style, by Sean Fitzpatrick, based on the precalculus text by Stitz and Zeager. He has also adapted the APEX Calculus texts to better suit the needs of his classes/students at the University of Lethbridge; see more of his work here.