There are a number of different minor scales available, suiting different situations and chord progressions. Two of the most common used by guitarists are the minor pentatonic (1-b3-4-5-b7) and ...
The Hungarian Gypsy scale is the fourth mode of the double harmonic scale, and is a great choice over minor/major 7th chords.
Harmonic minor keys are used when writing chords. There is another version of the minor key known as the melodic minor. This is used when writing a melody. Each key signature has two possible keys.