My DD's first finger food was firm tofu (not silken, the other kind). I just cubed it up and put it on her tray. She still loves tofu to this day!
Also, you can try polenta. You can fry it, which just firms it up, so when you cut it up into pieces, they stay in 1 piece all the way to his mouth, or leave it cold, which will have almost as good an effect, and then cube it.
You can do the same thing with cream of wheat. Cook it thick, then refrigerate to congeal, and either serve cold or cut into strips and fry.
Cubed cooked potatoes work best with a less starchy, more waxy potato like a yukon gold.
Lima beans are great, and other large beans (like fava, I think, but I still can't eat/order/cook them w/out thinking of "Silence of the Lambs"). Cook them enough and they mush in the gums, but maintain their structural integrity in the hand, between plate and mouth.
Seriously overcooked pasta.