Sausage casserole: bung a tin of chopped tomatoes in cooker, skin some sausages and cut up. Roll the pieces into balls with floury hands. Add to cooker. Cover with roughly chopped onions, mushrooms and carrots and some black pepper. Add enough water to almost cover the veg, switch on and forget for a few hours. Alternatively, use passata if you don't want the tomato lumps.
Cassoulet: takes a bit of prep (boiling dried haricots for 10 mins first but you have to do that with any cassoulet) but yummy. Put in a lot of pre-boiled haricots, add offcuts of meat (pork, lamb chops, cheap sausages, bits of fatty bacon) and onions, cover with lots of water and leave on for several hours. You can use meat you have no intention of eating (the original recipes use the beans to extract the juices and flavours from the meat and then ditch the scraggy bits) and then add a few bits you do want (usually confit of duck) halfway through cooking if you're in! You can add tomato puree too, and also cloves (though not too much or they dominate!). This is a recipe which doesn't seem to suffer from overcooking. Before slow cookers, I used to cook it in the over overnight (and was responsible for me getting a Le Creuset casserole dish as I wanted one to go on the hob and in the oven. Now I have rather more Le Creuset...)
I once bought some tinned cassoulet and threw it out as it seemed to be 90% fat. So I always use fairly lean white meats, but that's only personal preference.
Pork Shoulder casserole: again one for mushrooms, carrots, other winter veg, onions and pieces of pork shoulder. I prefer diced but you can just bung shoulder steaks in.
Pot Roast Chicken
Bung chicken in whole, add about a pint of water, surround with some veg etc and season. Switch on low and leave several hours. Be prepared for it to fall to bits!
My only 'don't' is to say never add potatoes, at least for the long cook. I always find they go bitter for some reason. If it's just for the last 20 mins, eg, cubed spuds in a beef/veg casserole with dumplings, then you can add the potatoes, shove the heat to maximum, bring it to the boil and then balance suet dumplings on top to steam. Delicious. (Even if I don't eat beef any more, I remember my mum's winter stews...)