The bracha on rice cakes according to most poskim is borei pri hoadomo. The reason is because there is dispute if rice is indeed the mezonos or hoadomo. Although the accepted custom is to make mezonos on it, however here there are other considerations. The rice is puffed whole and never cooked or disintegrated (slightly) as when it is cooked, therefore it is like eating it whole, and even when eating whole wheat kernels the bracha would be hoadomo.
The bracha on corn cakes is hoadomo, like all corn, whether it is eaten whole or not.
The bracha achrona on both of them is borei nefashos.
O:CH 208-4 and 7 Mibais Halevi vol.15 pg. 65, V’zos Haberacha Birurei Halacha 19-2 in the name of R’ S. Z. Auerbach, R’ Sheinberg zt”l and R’ M. Shternbuch shlit”a, Orh L’tzion 14-21, Sharrei Habracha pg 661, 662.