I play with drop D sometimes and it's fun, a lot of bands like System of a Down use it. Quick way to drop D is tune 12th fret harmonic on the sixth string to an open fourth string.

Drop C is fun too... even lower. Tune to drop d, then drop 1-5 strings down a step too, then drop D down a step to D.

That's probably a terrible explanation. I found it gets in the way of progressing with the basics when I spend time messing with tuning though!