Generate a unique id

Why not just use ToString?

public string generateID()
{
    return Guid.NewGuid().ToString("N");
}

If you would like it to be based on a URL, you could simply do the following:

public string generateID(string sourceUrl)
{
    return string.Format("{0}_{1:N}", sourceUrl, Guid.NewGuid());
}

If you want to hide the URL, you could use some form of SHA1 on the sourceURL, but I’m not sure what that might achieve.