public static class GooglePageRank
        {
            private static void Mix(ref uint a, ref uint b, ref uint c)
            {
                a -= b;
                a -= c;
                a ^= c >> 13;
                b -= c;
                b -= a;
                b ^= a << 8;
                c -= a;
                c -= b;
                c ^= b >> 13;
                a -= b;
                a -= c;
                a ^= c >> 12;
                b -= c;
                b -= a;
                b ^= a << 16;
                c -= a;
                c -= b;
                c ^= b >> 5;
                a -= b;
                a -= c;
                a ^= c >> 3;
                b -= c;
                b -= a;
                b ^= a << 10;
                c -= a;
                c -= b;
                c ^= b >> 15;
            }

            private static string GoogleChecksum(string url)
            {
                uint GoogleMagic = 0xE6359A60;

                uint a, b;
                uint c = GoogleMagic;

                a = b = 0x9E3779B9;

                int k = 0;
                int length = url.Length;

                //Algorithm
                while (length >= 12)
                {
                    a += (uint)(url[k + 0] + (url[k + 1] << 8) + (url[k + 2] << 16) + (url[k + 3] << 24));
                    b += (uint)(url[k + 4] + (url[k + 5] << 8) + (url[k + 6] << 16) + (url[k + 7] << 24));
                    c += (uint)(url[k + 8] + (url[k + 9] << 8) + (url[k + 10] << 16) + (url[k + 11] << 24));

                    Mix(ref a, ref b, ref c);

                    k += 12;
                    length -= 12;
                }

                c += (uint)url.Length;

                //All cases fall through
                switch (length)
                {
                    case 11:
                        c += (uint)(url[k + 10] << 24);
                        goto case 10; //fall through
                    case 10:
                        c += (uint)(url[k + 9] << 16);
                        goto case 9;
                    case 9:
                        c += (uint)(url[k + 8] << 8);
                        goto case 8;
                    case 8:
                        b += (uint)(url[k + 7] << 24);
                        goto case 7;
                    case 7:
                        b += (uint)(url[k + 6] << 16);
                        goto case 6;
                    case 6:
                        b += (uint)(url[k + 5] << 8);
                        goto case 5;
                    case 5:
                        b += (uint)(url[k + 4]);
                        goto case 4;
                    case 4:
                        a += (uint)(url[k + 3] << 24);
                        goto case 3;
                    case 3:
                        a += (uint)(url[k + 2] << 16);
                        goto case 2;
                    case 2:
                        a += (uint)(url[k + 1] << 8);
                        goto case 1;
                    case 1:
                        a += (uint)(url[k + 0]);
                        break;
                    default:
                        break;
                }

                Mix(ref a, ref b, ref c);

                return string.Format("6{0}", c);
            }

            public static int getPageRank(string url)
            {
                //Calculate URL checksum
                string checkSum = GoogleChecksum("info:" + url);
                string file = "http://toolbarqueries.google.com/search?client=navclient-auto&ch=" + checkSum + "&features=Rank&q=info:" + url;

                try
                {
                    //Request PR from Google
                    WebRequest request = WebRequest.Create(file);
                    WebResponse response = request.GetResponse();

                    StreamReader reader = new StreamReader(response.GetResponseStream());
                    string data = reader.ReadToEnd();

                    reader.Close();
                    response.Close();

                    //Parse PR from string
                    int pageRank = -1;
                    if (data.IndexOf(':') != -1)
                    {
                        data = data.Substring(data.LastIndexOf(':') + 1);
                    }

                    int.TryParse(data, out pageRank);

                    return pageRank;
                }
                catch (Exception)
                {
                    return -1;
                }
            }
        }

GooglePageRank - Class to get PageRank info for a URL

C#