From the Doctor: Prescription drugs like Ambien, Lunesta, and Sonata can recalibrate work- or happy-hour-altered sleep schedules, but they're best used short-term. Ambien, for example, targets receptors that inhibit brain activity, thereby sedating you. Many people find this very helpful and experience few side effects. Some people lose memory for the night and end up unconsciously raiding their refrigerators, having sex, or, after mixing Ambien with wine, ripping off their shirts and threatening to commit suicide, as a British man did on a transatlantic flight in 2005. If you're just having trouble drifting off, try Rozerem, which shortens the time it takes to fall asleep, doesn't sedate you, and doesn't make you psychologically dependent (oh, yeah—Ambien, Lunesta, and Sonata can do that, too).
From the Counter: Tylenol PM and Benadryl make you sleepy with antihistamines, but they can leave you groggy the next day. "Benadryl doesn't consistently work, and it has more side effects in many people than prescription drugs," says Dr. Jerrold A. Kram, of the California Center for Sleep Disorders.
From Nature: The most popular natural sleep aid is FDA-unapproved melatonin, the hormone our bodies produce when it's dark outside. While melatonin doesn't sedate you, it helps your body recognize when it's nighttime—useful if you work late on a computer or are trekking through Alaska in July. Another popular natural aid, valerian root, hasn't held up in clinical tests.
From the Cow: Warm milk: probably a placebo; tastes good with honey.