If what gai mentioned doesnt yield satisfactory results your only option is to redo the model but with more triangles, although thats usually really tedious so only do it if you really need to.
If youve got a bit of cash to spare it might also be worth checking out the subd and smooth plugin, i reckon itd be pretty useful for the sort of things youve shown already, and its very good at getting smooth surfaces.
subd and smooth: http://www.smustard.com/script/SubdivideAndSmooth