The Date class in ruby provides an upto method, so you can iterate over a series of dates.

Date.new(2000,1,1).upto( Date.new(2001,1,1) ) do |d|
    puts d
end

This counts by days, so it will print 365 values or so from 2000-01-01 to 2001-01-01.

What if you want to count by months? Being able to modify classes in Ruby makes this easy enough. Not sure this handles all situations, but it worked for what I needed.

class Date
    def +(n)
        if n == 0 then
            return self
        elsif self.month + n > 12
            return Date.new(
                            self.year + (n.to_f / 12).ceil, 
                            (self.month + n) % 12,
                            self.day
                           )
        else
            return Date.new(self.year, self.month + n, self.day)
        end
    end

    def upto(max)
        date = self
        until date > max do
            yield date
            date = date + 1
        end
    end
end

Date.new(2000,1,1).upto( Date.new(2001,1,1) ) do |d|
    puts d
end