Time::DATE_FORMATS.merge!(
  :default => lambda { |time|
    if time.year == Time.now.year
      if time.to_date == Time.now.to_date
        time.strftime("%I:%M %p").sub(/^0/, "")
      else
        time.strftime "%b #{time.day.ordinalize}"
      end
    else
      time.strftime "%b #{time.day.ordinalize}, %Y"
    end
  },
  :long => lambda { |time|
    time.strftime "%B #{time.day.ordinalize}, %Y"
  },
  :medium => lambda { |time|
    time.strftime "%b #{time.day.ordinalize}, %y"
  },
  :short => lambda { |time|
    time.strftime "%B #{time.day.ordinalize}"
  },
  :time => lambda { |time|
    time.strftime("%I:%M %p").sub(/^0/, "")
  }
)

then call @foo.created_at in yr view and will use the :default format. @foo.created_at.to_s(:long), etc for the others.