This includes:

Broccoli
Kale
Bok Choy
Swiss Chard
Brussel Sprouts
Cabbage
Cauliflower

Ideas for bringing crucifers into your diet:

Broccoli seeds can be sprouted in a few days and have the most powerful anticancer agents per ounce. Be sure to buy seeds which are sold for sprouting, not planting.

Broccoli tops are the most beneficial part of the plant, these can be diced finely when raw and added to guacamole as a healthy extender. Also eaten raw with a healthy dipping sauce. Broccoli could be eaten raw in slaw type salads as   well. Try to eat some raw as some of the anticancer agents are significantly diminished by cooking even slightly.

Kale can be cooked in stews or eaten raw on sandwhiches.  

Bok Choy is most often used in Chinese dishes - a simple one is a stir fry with tofu and Chinese mushrooms (such as shitake) in a light soy sauce or oyster sauce.

Swiss Chard can be stir fried with olive oil, garlic, lemon or vinegar, soy sauce or salt, and chili if you like.

Brussel Sprouts are also good steamed, stir fried or stewed.

Cabbage can be eaten in slaws, used as wrappers for other ingredients and baked or steamed, stir fried, or eaten canned as in saurkraut.