I've been working through these lately on guitar and fretless bass
(and I can't wait to have the time to rip the frets out of a cheap strat I have
to replace the frets on it , as well)

they are the basic Arabic Maqams or scales

www.maqamworld.com/maqamindex.html

There is a fantastic book on the Arabic Maqams that is really easy to understand and learn from
AND it comes with two CDs so that you can here the differences between the different
pitches (especially when playing a fretless instrument where one can make use of the
few quarter tones that exist in some Arabic scales). It costs $32.85 which is a fantastic deal
considering that it costs less than a single guitar lesson from someone. You can't even buy
two regular CDs for that price these days, let alone a great instructional book.

Since these are mostly minor scales, minor scales with additions and suspended scales,
I've found that they've really helped me because they are so comparable to the
Pythagorean modes of Western Music.

www.maqamworld.com/maqamindex.html