I highly recommend "Edly's Music Theory for Practical People". It's very much what I wish had been available when I was teaching full-time decades ago. I like it because:
A. It doesn't assume you play piano
B. It doesn't assume you know how to hear written standard notation
C. It doesn't require you to read standard notation, but makes the point that reading is one very powerful and useful part of understanding the language of music
D. It doesn't presume that western classical music is the only music that exists
E. It has wonderfully clear diagrams- so many of them are exactly what I wound up han-writign for my students back in the '80s.
Here's the link...
http://www.edly.com/mtfpp.html
