Which vegetables to use for stock? Which vegetables and/or fresh herbs should be used when making vegetable stock?

Are there any vegetables/herbs that should be avoided?

Can parts of vegetables that would otherwise be discarded be included (eg. potato peel, carrot tops, onion skins)?
Typically veggies are onions, carrots, celery, leeks, garlic, shallots, etc. Throw in some peppercorns, also, and a Bouquet garni. You can add most other veggies, too, and mushrooms, but avoid adding things that give a strong (bad) flavour after cooked for a long time (broccoli, brussels sprouts, cauliflower, etc.).