Truncate NSDate (Zero-out time)

unsigned int flags = NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay;
NSCalendar* calendar = [NSCalendar currentCalendar];
NSDateComponents* components = [calendar components:flags fromDate:date];
NSDate* dateOnly = [calendar dateFromComponents:components];

date is the date you want to remove the time from.

This separates the date and time and creates a new date with the default time (00:00:00).

EDIT

To take time zone into account:

NSDate* dateOnly = [[calendar dateFromComponents:components] dateByAddingTimeInterval:[[NSTimeZone localTimeZone]secondsFromGMT]];