We just had our third child 3 weeks ago. Our previous children are now 6 and 3. Boy, were we missing out without the Halo Sleep Sack.
We discovered it when the hospital dressed our newborn in it. The picture on this site doesn't show it, but the most amazing thing is the velcro "wings" that swaddle your baby. With our two previous kids, we had to wrap them in blankets. I was not nearly as good at that as my wife, but even when she did the swaddling, any movement by the child would cause them to come unwrapped. As any parent would know, once a newborn is no longer confined they will wake up.
The "wings" of the sleep sack keep the baby swaddled all night long. This allows them (and you) to get a good night's sleep.
These are a bit expensive, but they are worth every penny. I guess the Halo company is allowed to make some money off of this great idea!