PHP code for generating decent-looking coupon codes (mix of letters and numbers)

$chars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
$res = "";
for ($i = 0; $i < 10; $i++) {
    $res .= $chars[mt_rand(0, strlen($chars)-1)];
}

You can optimize this by preallocating the $res string and caching the result of strlen($chars)-1. This is left as an exercise to the reader, since probably you won't be generating thousands of coupons per second.

Try this:

substr(base_convert(sha1(uniqid(mt_rand())), 16, 36), 0, 10)