Mysql DATETIME evaluation: Get all records whose value is before midnight of the current day (basically yesterday and before

This is really simple yet I always struggle with it. I need help getting records before midnight:

 AND last_checked < date('2013-06-25 00:00:00'))

This obviously doesn't work, since its string evaluation. I do not want to restrict it to this year and put a between in the code. Any help is extremely appreciated :)