This one escapes me everytime I need which results to much googling. The function is to convert SQL datetime value to human-readable format.
* Converts the likes of '2010-08-01 14:57:15' to 'August 1, 2010, 2:57 pm'
$datetime_value ="2010-08-01 14:57:15";
echo date( "F j, Y, g:i a", strtotime( $datetime_value ) );
Here's another example which you will see on some of my templates.
<?php echo date('Y-m-d', strtotime('next month')); ?>
For more formats, go head to PHP Doc.