"An Introduction to Mathematical Reasoning" by Peter J Eccels. Teaches the vocabulary of mathematics, just the basics you need to think like a mathematician, not a mathematics user like most science texts.

"How To Solve It" George Polya. Heurists and problem solving skills, by a great mathematician.

Do a google search, specially in the sci.math newsgroup. Again, read books by mathematicians for mathematicians; they're often far more enjoyable and actually far more straightforward (I was often confused by the examples in my school work; I didn't care for "vehicle moving at speed X" or "object falling at from height Y". We all have a different internal visual mind and I tended to think in abstract patterns, usually colors, lines or nested bodies, without real physical objects distracting me.)