Here is another good article by By Elizabeth Pantley who is a mother, author, speaker and parenting expert.
If your baby cries inconsolably for long periods every day, particularly at the same time each day, he may have colic. Researchers are still unsure of colic's exact cause. Some experts believe that colic is related to the immaturity of a baby's digestive system. Whatever the cause, and it may be a combination of all the theories; colic is among the most exasperating conditions that parents of new babies face.
Colic occurs only to newborn babies, up to about four to five months of age. Look for patterns to your baby's crying; these can provide clues as to which suggestions are most likely to help. Then experiment with some of the ideas in the following list and in the rest of this article:

If breastfeeding, feed on demand (cue feeding), for nutrition as well as comfort, as often as your baby needs a calming influence.

If breastfeeding, try avoiding foods that may cause gas in your baby, such as dairy products, caffeine, cabbage, broccoli and other gassy vegetables.

If bottlefeeding, offer more frequent but smaller meals; experiment with different formulas with your doctor or health care provider's approval.

If bottlefeeding, try different types of bottles and nipples that prevent air from entering your baby as he drinks, such as those with curved bottles or collapsible liners.

Hold your baby in a more upright position for feeding and directly afterwards.

Experiment with how often and when you burp your baby.

Offer meals in a quiet setting.

If baby likes a pacifier, offer him one.
Invest in a baby sling or carrier and use it during colicky periods.

If the weather's too unpleasant for an outside stroll, bring your stroller in the house and walk your baby around.

Give your baby a warm bath.

Hold your baby with her legs curled up toward her belly.

Massage your baby's tummy, or give him a full massage.

Swaddle your baby in a warm blanket.

Lay your baby tummy down across your lap and massage or pat her back.

Hold your baby in a rocking chair, or put him in a swing.

Walk with Baby in a quiet, dark room while you hum or sing.

Try keeping your baby away from highly
stimulating situations during the day when possible to prevent sensory overload.

Lie on your back and lay your baby on top of your tummy down while massaging his back. (Transfer your baby to his bed if he falls asleep.)

Take Baby for a ride in the car.

Play soothing music or turn on white noise such as a vacuum cleaner or running water.

As a last resort, ask your doctor or health care provider about medications available for colic and gas.