Large potatoes, cut into eigths, carrots, green bell pepper, onion wedges, whole mushrooms.
FWIW, I use Campbell’s Cream of Mushroom Soup and Lipton Onion Soup Mix to season the roast. It’s the way dad made it, and I always liked dad’s pot roast.
The basic pot roast veggies in this household are potatoes, carrots, onions, and celery. If we happen to have a turnip in the house, then I’ll throw it in as well, same with mushrooms. All veggies are cut into chunks, and peeled if appropriate. I generally make some beef broth with Better than Bouillon beef or vegetable base, and pour that over everything. This gets cooked in the oven.
I also make what we call a chicken pot roast. I peel and slice potatoes, and lay them in the bottom of the roasting pan. I prepare a whole chicken by removing the giblets and putting them in the fridge, then removing the excess fat. I loosen the skin on the breast, and put the fat and some seasonings in that area (thus, the chicken becomes self-basting). Then I put about a half of an onion and a quarter of a carrot and celery stalk in the main cavity. I put about a quarter of an onion in the neck cavity. I put the chicken on top of the potatoes and sprinkle with poultry seasoning. I peel carrots and onions, and chop them up, and put them and some celery around the chicken. I roast this, covered, for a couple of hours at about 350. The chicken flavors the potatoes most wonderfully, and the other veggies flavor the chicken. I generally pick the bits of meat from the carcass and make chicken soup the next day with the skin and bones.
Sometimes during the winter I will peel and chop up potatoes, carrots, onions, celery, and maybe a turnip, put them in an oven dish, put some chicken broth in it, toss the veggies to coat, and then roast. This is a very satisfying vegetable dish, and it doesn’t need any fat, other than the fat in the chicken broth. Some people might like some black pepper with it, but we enjoy it without any other seasoning.
Sometimes I make a pot roast in the slow cooker, and then I only put chopped onions in it. The slow cooker doesn’t do a great job on vegetables, so we will have some other sort of veggies if I make a roast that way.
I second the mushrooms, but try this variation: saute them (whole or halved) briefly in butter and garlic before putting them and the rest of the ingredients in the cooking vessel of your choice.For the liquid: Sam’s Club sells an item called Tone’s Beef Base–kind of a reduced beef stock you add water to. It’s not as salty as bouillon cubes, and a large jar sell for less than $3 and lasts a long time. Reconstitute, add seasonings of your choice and a splash of Worcestershire sauce, pour over meat and veggies, cook and enjoy. YUMMMMMMM! 
eggplant and leeks
Potatoes, baby carrots, onions, garlic, salt and ground pepper. We usually do “Roast In A Bag” which comes with its own seasoning pouch. You mix it with water and pour it over the contents. Makes a nice, small amount of beef flavored gravy for the whole affair to roast in. Yum!
I thought I’d mention that we were watching Emeril one night, preparing a roast. He cut little slits in it, and stuffed in a clove of garlic. You can do this as many times as you like, on both sides of the roast. We tried it, and it was amazing! If you like garlic, I recommend that you try this sometime with a roast.
Alton Brown uses olives and raisins. Also, he uses a foil pouch in the oven.
I like to use a good inexpensive barbaronne red a buddy introduced me to. Very drinkable, let me rummage in the fridge for the name=)
<quick run to kitchen and back>
Opici vinyards. Fairly inexpensive, but tasty.
I also add a bouquet garni of parsley, bay leaf, thyme, marjoram, rosemary and black pepper wrapped in gauze/cheesecloth. I also prefer to use the crockpot as it is convenient and lets me use the oven for baking.