All of you people with "too much grain" in the basement are welcome to drop it off here. Seriously. (I've found oat and oatmeal, barley grits, corn, buckwheat, and of course rice - but nothing else.)
I have a German mixer / food processor "machine" (Bosch MUM 6612, somewhat comparable to a KitchenAid) with a grain mill that has to be attached on top of the mixing bowl. So the ground grains will end up where you need them anyway. I've had this model for almost 12 years now and I like it.
From what I know metal grinders won't grind corn but anything else, including oil seeds (sesame, poppy), you can and should clean them regularly. Stone grinders won't do oil seeds but are sturdier and can also do corn. Usually they're not supposed to be cleaned on a regular basis.
If you're planning on baking with whole grains on a regular basis I'd recommend an electric grinder. Sure, it's not quite as "eco" as hand-grinding grains but it'll be a big help in actually getting the job done. (I know, you already said you were looking for an electrical grinder.)