These are the strings I most often recommend for Drop C, and they work well for lower tunings as well if you don't mind your strings being a tad slinky. If you've never played a set optimized for drop tunings, you don't know what you've been missing. Finally, you'll see what it's like to have balanced tension, even when you tune down.
Gauges: .011 - .014 - .018p - .032 - .044 - .058