Exercises that require no equipment

Are there any excercises that really don't require equipment. I'm talking about things like crunches and sit ups. Anything that works a certain muscle or group of muscles. I'm in a dorm and don't have money to buy weights or really any equipment.

Look up "core exercises" on wikipedia or google. They don't get you bulky (only weights will do that), but they'll get you fit in no time.

push ups, crunches, and pull ups are all very helpful

Wanking.

Heavy breathing