Two other ways, if anyone's interested:
Chromatic Mediant, which I just found out about.
And Chromatic Alteration, which is somewhat like what Nikolas mentioned (I think), and is a good way to go from parallel major/minor to minor/major. The difference is that in Nikolas', the chromaticism is just in one voice, i.e. G-B-D->E-G#-B->A-C-E; G to G# to A.
However, in Chromatic Alteration, two chords are used, one in the old key and one in the new, that are almost the same. The only difference is one is altered by a semitone. For example, from G Minor to G Major, the G Minor chord is G-Bb-D and the G Major chord is G-B-D; exactly the same, only the third of the chord is raised by a half step. Therefore, you can use that to modulate into the new key.