Hugamonkey sling carrier - I have a simple black pouch sling (sometimes referred to as a peanut sling). It's ridiculously easy to use, lightweight (good for warm weather and travel,and other peanut slings I've tried have been a bit thicker and so heavier/bulkier), and very reasonably priced (under $29). I particularly like to use it in the hip-carrying position.
Admittedly, though, it's a little hard on your back/neck/shoulders when your baby starts to get heavy, so I don't necessarily recommend using it solely when your baby gets to be over 12lbs or so.
*Note: I have to admit I've been a little obsessed with finding the perfect baby carrier for every stage of my baby's growth because I am an adoptive mother and want to carry my baby as much as possible for attachment and bonding purposes. This sling carrier fit the bill when I wanted to hold my baby hands-free with a hipseat carrier.