I accidentally kicked a bed post with my left foot. it's bruised and hurts a lot. need an x-ray?

Depends: If the bruising and pain are limited to the toes, then probably not. Most toe fractures are treated with a hard soled shoe. If there is obvious deformity of the toes, get it checked out. It the pain and bruising extends into the main portion of the foot, then yes, see a doctor. Finally, if there is any doubt, get it checked out. Sometimes the best thing doctors provide is peace of mind.

Xray: If this occurred late at night an x ray can probably wait until the morning if the foot is still painful. Typically, the tip of the phalange (toe) may be sprained but on occasion there can be a fracture.