I heard LINQ is the new black, so here's my attempt using LINQ:

private static Random random = new Random();
public static string RandomString(int length)
{
    const string chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
    return new string(Enumerable.Repeat(chars, length)
      .Select(s => s[random.Next(s.Length)]).ToArray());
}

(Note: The use of theRandom class makes this unsuitable for anything security related , such as creating passwords or tokens. Use the RNGCryptoServiceProvider class if you need a strong random number generator.)