var postData = {
    username: 'test',
    words: 'hello world'
};
$.ajax({
    url: 'http://www.cnblogs.com/api/say',
    data: postData,
    type: 'post',            
});

$url = 'http://www.cnblogs.com/api/say';
$data = array('username' => 'test',
              'words'    => 'hello world');

$data = http_build_query($data);
 
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, $data); 
$response = curl_exec($ch);
curl_close($ch);

var postData = new
{
    username = "test",
    words = "hello world"
};

static void Main(string[] args)
{
    var url = "http://www.cnblogs.com/api/say";

    var postData = new
    {
        username = "test",
        words = "hello world"
    };

    var webRequest = WebRequest.Create(url) as HttpWebRequest;
    webRequest.Method = "post";
    webRequest.ContentType = "application/x-www-form-urlencoded";

    var queryString = string.Join("&",
                        from p in postData.GetType().GetProperties()
                        select p.Name + "=" + HttpUtility.UrlEncode(p.GetValue(postData, null).ToString()));

    using (var sw = new StreamWriter(webRequest.GetRequestStream()))
    {
        sw.Write(queryString);
    }

    using (var response = webRequest.GetResponse())
    {
        using (var sr = new StreamReader(response.GetResponseStream()))
        {
            Console.WriteLine(sr.ReadToEnd());
        }
    }
}

var postData = new Dictionary<string, string>
{
    { "username", "test" },
    { "words", "hello world" }
};

static void Main(string[] args)
{
    var url = "http://www.cnblogs.com/api/say";

    var postData = new Dictionary<string, string>
    {
        { "username", "test" },
        { "words", "hello world" }
    };

    var urlEncodedContent = new FormUrlEncodedContent(postData);
    var httpClient = new HttpClient();
    var result = httpClient.PostAsync(url, urlEncodedContent).Result.Content.ReadAsStringAsync().Result;
    Console.WriteLine(result);
}