Well its very simple in controller you have somthing like this:
-- Controller
ViewBag.Profile_Id = new SelectList(db.Profiles, "Id", "Name", model.Profile_Id);
--View (Option A)
@Html.DropDownList("Profile_Id")
--View (Option B) --> Send a null value to the list
@Html.DropDownList("Profile_Id", null, "-- Choose --", new { @class = "input-large" })