Most of them are not worth it. In that the organ meat of the animal is rarely any better than the main muscle meat. Of course if you are in to hunting and getting the most food from your kill then they have value. But as someone who lives a more urban lifestyle I prefer those parts of the animal to be used for dog food and fast food.
That said, some are worthy in their own right
Goose Live (Foi Gras) fantastic, rich and mildly meaty substance.
Duck Liver, like goose liver.
Beef Liver, very strong, not to my personal liking, but has a flavour that you won’t find elsewhere.
Pork Liver, strong, used frequently in Pate. Not to my taste as I prefer the milder but equally ritch goose and duck liver based pates.
Suet (the fat arround a Cow or Sheeps kidneys) a wonderfull and tasteless fat, makes some of the best pastry types.
Marrowbone, rich and soft texture, like good pate without the ‘liveryness’ of pork liver based pate flavours.
Tongue, in most mamals this is one of the largest muscles, and completely boneless, makes for excellent eating.
Skin, OK not an internal organ, but often overlooked becuse of the large fat deposits under almost all animals skin, still when cooked hard to reduce the fat it can be excellent. Chinese style crispy duck skin is truely fantastic eating.
A few others have uses due to their consistancy and lack of flavour that makes them worthwhile, but they aren’t favoured for their flavour. Such as stomach cawl, and natural sausage skins.