From http://schroedman.wordpress.com/2012/01/19/short-unique-id-in-c-without-using-guid/

new_gist_fileshort-unique-id-in-c-without-using-guid.cs

static string uniqueCode()
{
    string characters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789!@#";
    string ticks = DateTime.UtcNow.Ticks.ToString();
    var code = "";
    for (var i = 0; i < characters.Length; i += 2)
    {
        if ((i + 2) <= ticks.Length)
        {
            var number = int.Parse(ticks.Substring(i, 2));
            if (number > characters.Length - 1)
            {
                var one = double.Parse(number.ToString().Substring(0, 1));
                var two = double.Parse(number.ToString().Substring(1, 1));
                code += characters[Convert.ToInt32(one)];
                code += characters[Convert.ToInt32(two)];
            }
            else
                code += characters[number];
        }
    }
    return code;
}