cow's tongue is delicious. many a spanish recipe for tongue.
calf's liver.. when cooked in butter and garlic with a squeeze of lemon.. can make the liver taste mild.. very good.
chicken gizzards/heart packages are good for the crockpot. make a savory gravy and cook until tender.
oxtail is expensive.. it tastes like brisket meat, because it's cooked up against the bone, which makes it very tender.
another one for the crockpot and a savory gravy..
beef cheeks. two ways to cook this. in a crockpot. BUT, timing is everything. after 4 hrs, it can have the texture of brisket. longer and you can shred it and make beef tacos or enchiladas..
pig's head.. roasted. this was a delicacy in the early centuries.. can be a delicacy now, but labor intensive. full of collagen. make head cheese out of the meat from the head.
pig's feet.. so good and full of collagen. many spanish recipes have "trotters" cooked with beans.. ham and bean soup is one.. or cook down and add greens.

so many good parts of the animal.. so many good recipes. usually the cheaper cuts of meat - or used to be.

and these cuts of meat usually have more fat, which America shy's away from, now.