I personally don't think Riggot is good enough to improve the team despite him playing well on Saturday morning. Gareth Southgate is a good and experienced defender along with being a good communicator and Riggot isn't the first central defender to look better than the sum of his parts playing alongside the ex-England man.
Clearly we need a central defender or two and they must fit into one of two categories. Either they must be young and inexperienced enough to accept being third choice, or they must be good enough to go into the team straight up. Riggot seems to me to be neither, while Anton Ferdinand probably wouldn't accept a place on the bench either given that he is playing regularly for West Ham.
My preferred choice would be Ledley King. Those that don't rate him or think he is worth the money (those posters are significantly diminishing from when I first mentioned him) are entitled to their view. I'm pleased to see Banana has stuck to his guns, I remember he found it absolutely unbelieveable and laughable last season when I said that IMHO King would cost more than Gallas. I still think he would. One reason is obviously because he is English, the other is that he is a better player.
If you are going to go for inexperienced cover, now that Dawson has gone then Hobbs along with an Agger or someone similar is the call.