The Moby
We used this thing from 0 - about 7 weeks. It's in essence a long (19 feet?) stretchy knit wrap made of cotton. It's nice because it keeps you incredibly close to baby. There's a little bit of a learning curve on how to use it, but once it's learned, it's pretty easy to do, in my opinion. Plus, you can put on this carrier before putting baby in it. It costs about 35 or so bucks, but if you're low on cash, you can also DIY it. Machine-washabe is always a plus. Drawbacks? You can only use to to about 15 lbs before the supportiveness really drops off - this is due to the stretchiness of the material. It's not really ideal for carrying older infants (largely because the weight limit really limits you from more comfy carries like back carries). It also keeps you REALLY hot, so not great for summer. Still though, in my opinion a nice starter wrap. For serious wrappers, you may want to start out with something like woven wrap, which you can eventually use for back carries and other things...but only if you're willing to spend lots of $$$.
The Beco Gemini
Our life (and sanity) saver! we used this from age 7 weeks to 13 months. It first babies 7-35 lbs. You could actually use this from birth and on (without a special infant insert). I loved this carrier because you can face baby in, out (for sort periods of time), on your back, and on your hip. So many options! Plus, the seat can convert from narrow (for newbies) to wide (for most sizes of babies) for better seating arrangements. We took this thing literally everywhere with us. SO useful. The safety buckles on this thing are tricky at first, but once you've used it a few times, they are not so bad.
The Kinderpack Standard
Around 13 months, it was getting obvious that the Beco was getting too small. AJ's legs are ridiculously long and I'm told that the Beco was meant for somewhat smaller infants anyway. Soooo, I did the research on toddler carriers. What I found was that the majority of moms who were still wearing toddlers were using either 1) woven wraps or 2) Tula carriers. Someone recommended Kinderpack, but I sort of ignored them (not a big name, can't be THAT good right?). As I started looking and comparing toddler carriers, I started to find many recommendations to consider a KP standard carrier instead. What I think many moms don't know (me included) is that most toddler carriers are made for children who are a minimum of 25 lbs. What this translates to, is if your child is right around 25 lbs, there's a good chance he'll still be "swimming" in a toddler sized carrier. Long story short(er) we decided to buy a Kinderpack standard (meant for babies 8+ months). It fits BEAUTIFULLY. He's completely supported knee-to-knee now, and has room to grow. The pack also comes with a Koolnit panel down his back, which is nice because it keeps the summer heat from getting to him. My only slight dissatisfaction so far is the PFAs (perfect fit adjusters) - they seem a lot stickier than the Beco ones. Oh well, maybe I'll get used to it.