Try this:
var request = (HttpWebRequest)WebRequest.Create("http://www.example.com/recepticle.aspx");
var postData = "thing1=hello";
postData += "&thing2=world";
var data = Encoding.ASCII.GetBytes(postData);
request.Method = "POST";
request.ContentType = "application/x-www-form-urlencoded";
request.ContentLength = data.Length;
using (var stream = request.GetRequestStream())
{
stream.Write(data, 0, data.Length);
}
var response = (HttpWebResponse)request.GetResponse();
var responseString = new StreamReader(response.GetResponseStream()).ReadToEnd();