I've provided the same answer on another post. Shortening it:
$date = new DateTime('tomorrow -1 month');
// lists() does not accept raw queries,
// so you have to specify the SELECT clause
$days = Object::select(array(
DB::raw('DATE(`created_at`) as `date`'),
DB::raw('COUNT(*) as `count`')
))
->where('created_at', '>', $date)
->group_by('date')
->order_by('date', 'DESC')
->lists('count', 'date');
// Notice lists returns an associative array with its second and
// optional param as the key, and the first param as the value
foreach ($days as $date => $count) {
print($date . ' - ' . $count);
}