You could always remove the element that you selected the first time round, then you wouldn't pick it again. If you don't want to modify the array create a copy.

 for ($i=0; $i<2; $i++) {
    $random = array_rand($my_array);  # one random array element number
    $get_it = $my_array[$random];    # get the letter from the array
    echo $get_it;

    unset($my_array[$random]);
 }

What about this?

$random = $my_array; // make a copy of the array
shuffle($random); // randomize the order
echo array_pop($random); // take the last element and remove it
echo array_pop($random); // s.a.

array_rand() can take two parameters, the array and the number of (different) elements you want to pick.

mixed array_rand ( array $input [, int $num_req = 1 ] )

$my_array = array('a','b','c','d','e');
foreach( array_rand($my_array, 2) as $key ) {
  echo $my_array[$key];
}

foreach (array_intersect_key($arr, array_flip(array_rand($arr, 2))) as $k => $v) {
    echo "$k:$v\n";
}

//or

list($a, $b) = array_values(array_intersect_key($arr, array_flip(array_rand($arr, 2))));

Get the first random, then use a do..while loop to get the second:

$random1 = array_rand($my_array);
do {
    $random2 = array_rand($my_array);
} while($random1 == $random2);

This will keep looping until random2 is not the same as random1