It's certainly not perfect, but I came up with it under pressure in less than 90 seconds without checking online for the modulo return values, so I'm rather proud of it.

<?php

$x = 1;

while($x <= 100) {

if((($x % 5) == 0) && (($x % 3) != 0)){ print("Buzz"); }else{ if(($x % 3) == 0){ if(($x % 5) == 0) { print("FizzBuzz"); } else { print("Fizz"); } }else{ print($x); }} ++$x; }

?>