E.B.
My youngest began sleeping through the night at 3 months, it is actually not the age that determines this, but the babies weight. From a metabolic standpoint the infant needs to be at least 10lbs (typically a doc will recommend that the infant "double" it's birthweight). Anyway, I found success with the following:
1. Swaddle
2. White Noise (ocean sound)
3. Chicco Goodnight Stars (before EVERY nap/bedtime I play this so my son has the same routine and knows its time for sleep)
http://www.chiccousa.com/toys/newborn-2/goodnight-stars.aspx
4. Security stuffed animal (or blanket) I actually slept with it for a few days to get my smell and he thought I was next to him.
5. Pacifier. I would not let him "cry it out", not a fan, but I wouldn't go in there for every whimper. If it led to crying, I would give him a pacifier to eliminate a feeding. I also use all rubber pacifiers, they are really soft.