An entire online text for Precalc from the Univeristy of Houston.

[Brilliant!]

http://online.math.uh.edu/Math1330/index.html

It's the best free source I've seen. It's the project of grad students and is a comprehensive online text that has everything you'd expect from a textbook. And on top of that, there are streaming lectures.

[qntty]

University of Washington (http://www.math.washington.edu/~m120/) has a free precalc book too.

[Sankaku]

Very short Trig course:

http://www.clarku.edu/~djoyce/trig/