This method uses an instance of an encryption class (RNGCryptoServiceProvider). This class is better at not following a pattern when it creates random numbers.

RandomNumberGenerator.cs

public static class RandomNumberGenerator
{
    private static readonly RNGCryptoServiceProvider _generator = new RNGCryptoServiceProvider();

    public static int NumberBetween(int minimumValue, int maximumValue)
    {
        byte[] randomNumber = new byte[1];

        _generator.GetBytes(randomNumber);

        double asciiValueOfRandomCharacter = Convert.ToDouble(randomNumber[0]);

        // We are using Math.Max, and substracting 0.00000000001,
        // to ensure "multiplier" will always be between 0.0 and .99999999999
        // Otherwise, it's possible for it to be "1", which causes problems in our rounding.
        double multiplier = Math.Max(0, (asciiValueOfRandomCharacter / 255d) - 0.00000000001d);

        // We need to add one to the range, to allow for the rounding done with Math.Floor
        int range = maximumValue - minimumValue + 1;

        double randomValueInRange = Math.Floor(multiplier * range);

        return (int)(minimumValue + randomValueInRange);
    }
}