If you want to DO math, nothing beats working through a decent textbook. I have worked through several since I'm approaching 50 and don't use math enough to keep my skills up (and like any skill, you have to keep practicing to stay decently competent in math). The best Precalculus textbook I have used is Swokowski's "Algebra and Trigonometry with Analytic Geometry" which is clear, concise, and has lots of problems. If you want to learn ABOUT math, Davis and Hersch's "The Mathematical Experience" is a fairly easy read about philosophy of math, how it is used, and a bit about studying math. Eric Temple Bell's "Mathematics: Queen and Servant of Science" is a bit dated but an excellent history of math for someone interested in learning to do advanced math; the author's a bit biased towards algebra over analysis, number theory, and geometry, but not excessively so. Its biggest lack is only one short chapter on probability and statistics. This is not a particularly easy read since it covers things in some depth, but I think it is worth the effort.
Also recommended in this reply