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 written in the APEX Calculus style, by Sean Fitzpatrick. 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.