PHP

// Generate a random character string
function rand_str($length = 32, $chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890')
{
    // Length of character list
    $chars_length = (strlen($chars) - 1);

    // Start our string
    $string = $chars{rand(0, $chars_length)};

    // Generate random string
    for ($i = 1; $i < $length; $i = strlen($string))
    {
        // Grab a random character from our list
        $r = $chars{rand(0, $chars_length)};

        // Make sure the same two characters don't appear next to each other
        if ($r != $string{$i - 1}) $string .=  $r;
    }

    // Return the string
    return $string;
}