ToSentenceCase

/// <summary>
        /// Ensures the first character is a capital letter and following characters are lower case. Example: ToSentenceCase("hEllo") = "Hello"
        /// </summary>
        public static string ToSentenceCase(this string s)
        {
            if (s == null)
                return s;
            if (s.Trim().Length == 0)
                return s;

            var sb = new StringBuilder(s.Length);
            var parts = s.Split(" ".ToCharArray());

            for (int i = 0; i < parts.Length; i++)
            {
                char[] word = parts[i].ToCharArray();
                if (word.Length == 1)
                {
                    if (char.IsWhiteSpace(word[0]))
                    {
                        sb.Append(word[0]);
                        continue;
                    }
                }
                for (int j = 0; j < word.Length; j++)
                {
                    if (j == 0)
                        word[j] = char.ToUpperInvariant(word[j]);
                    else
                        word[j] = char.ToLowerInvariant(word[j]);
                }
                sb.Append(new string(word));
                sb.Append(" ");
            }
            return sb.ToString().TrimEnd();
        }