Three letter complete list

[eluser]Total Shop UK[/eluser]
I am trying to create a list that will contain every word using up to three letters.

a,b,c...z
aa,ab,ac...zz
aaa,aab,aac...zzz

Edit: worked it out but the other guys code looks cleaner

Code:

$letters=array('a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z');
$arr1=$letters;
$arr2=$letters;
$arr3=$letters;
foreach ($arr1 as $value1) {
    echo $value1."\r\n";
    foreach ($arr2 as $value2) {
        echo $value1.$value2."\r\n";
        foreach ($arr3 as $value3){
            echo $value1.$value2.$value3."\r\n";
        }
    }
}