Do you make your cakes with butter or marg? Marg often gives a better texture, but butter keeps and freezes better. Also, when you freeze the cake, wrap it first in clingfilm, freeze it, then overwrap it again in tinfoil within a day or two of freezing. For some reason they keep better that way.
I very much doubt you could freeze unbaked cake mixture because the raising action is caused by the raising agent reacting with moisture (as Bobs says), and by the time the mixture has frozen and defrosted the reaction will probably have gone too far and the cake won't rise in the oven. Also you'd probably have to remix the defrosted mixture, which would overmix the cake overall (IYSWIM).