Code:

using System;
using System.Linq;
using System.Text;
using System.Net;
using System.Collections.Generic;
using System.Collections.Specialized;
using HtmlAgilityPack;

namespace Crawler.Library
{
    public class WebCrawler
    {
        #region Private Methods

        private string GetHTMLText(string url, NameValueCollection parameters)
        {
            string htmlText = string.Empty;
            using (WebClient client = new WebClient())
            {
                Encoding encoding = Encoding.UTF8;
                client.Encoding = encoding;
                client.Headers.Add("user-agent", "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.0.5) Gecko/2008120122 Firefox/3.0.5");

                htmlText = encoding.GetString(client.UploadValues(url, "post", parameters));
            }

            return htmlText;
        }

        #endregion

        #region Public Methods

        public string GetMiddleExchangeRate(DateTime date)
        {
            string ret = string.Empty;
            try
            {
                string requestedDate = date.ToString("dd.MM.yyyy");
                string url = @"http://www.nbs.rs/internet/latinica/scripts/kl.html";

                NameValueCollection parameters = new NameValueCollection();
                parameters.Add("datum", requestedDate);
                parameters.Add("eksport", "html");
                parameters.Add("vrsta", "3");

                ret = GetHTMLText(url, parameters);

                HtmlDocument doc = new HtmlDocument();
                doc.LoadHtml(ret);

                HtmlNodeCollection nodes = doc.DocumentNode.SelectNodes("//td[@class='tablecell']");
                
                StringBuilder sb = new StringBuilder();
                foreach (HtmlNode node in nodes)
                {
                    sb.AppendLine(node.InnerText);
                }

                ret = sb.ToString();

            }
            catch(Exception ex)
            {
                ret = ex.Message;
            }

            return ret;
        }

        #endregion
    }
}

Code:

978
Evropska unija
EUR
1
94,8637
036
Australija
AUD
1
49,4185
...

Code:

Crawler.Library.WebCrawler crawler = new Crawler.Library.WebCrawler();

string rates = crawler.GetMiddleExchangeRate(new DateTime(2009, 4, 1));