There are so many baby gadgets out there and many of them are nice to have, a few of them you really need (like a carseat if you plan to go anywhere in a car). I don't know what I would have done without a baby carrier. Well, I would have done a lot less and had a rather unhappy baby more often. There are so many different kinds out there (stretchy wraps, woven wraps, soft structured, ring slings, mei tais, ...). I'll start with what I've used and what has worked for me.
My very first wrap/carrier was the Moby wrap, a soft and stretchy piece of cloth that is fat in the middle and narrower on the ends. I just knew it would be a good choice before I got it and was very happy to receive it as a shower gift. It does have a bit of a learning curve to learn to tie it on. Have someone show you or check out youtube. (While there are lots of great how to videos there, just be careful, I know there are how tos to put your baby on your back with the Moby, but you need a woven wrap for that). I would tie it on and put the baby in and out as needed. The Moby works great for keeping a small baby close. It was perfect for my daughter until she was about 15 pounds and then I needed more support for my back.
That brings us to woven wraps. They can be tied in many different ways. You can tie it similar to the Moby but put the baby in with it halfway and then tie the rest of the way (They are not stretchy). You can do back caries; I really like the rucksack carry. I have an Ellaroo and really like it. It is cooler than the Moby, so good for summer.
Another favorite carrier of ours is a soft structured carrier, the Ergo. If you can, try this on with baby. The different styles fit differently. We got the organic original style. The back of the performance style comes up higher on baby's back. The baby needs to be taller to fit this one. Our Ergo carrier works great even for long periods of time. The weight is supported on the hips and the shoulders.
I'm very happy with all three of these carriers. It would have been nice if the Moby lasted longer, but it really was great for my not so tiny newborn. My Little One likes them all too, but really its being held and snuggled up to me more than the carriers.