[AcceptVerbs(HttpVerbs.Post)]
    public ActionResult Login(FormCollection collection)
    {
        var users =
            (from p in _dataContext.Users
            where p.Name == collection["Username"] && p.Password == collection["Password"]
             select p);

        if (users.Count() > 0)
        {
            // Login Succeed
            // To get the username I should do something like users.First().Name
            // and that's really bad...

            return RedirectToAction("Login");
        }
        else
        {
            // Login Faild
            return View();
        }
    }

var user = _dataContext.Users.SingleOrDefault(p =>
                  p.Name == collection["Username"]
                  && p.Password == collection["Password"]);

if(user != null)
{
    // Go on...
    return RedirectToAction("Login");
}
else
{
    // Login Faild
    return View();