OK moog - links to slings.
I can't remember which ones I linked to originally, but here are some really good ones:
Firstly,
Since people have been discussing mobys, there are stretchy wrap slings eg moby, hugabub or any of the other brands - quite often TK Maxx get a load of stretchy wraps in ;)
These are great - I explained a bit about them above, but they have limited usefulness and when the baby gets heavier, they aren't supportive enough any more. Typically this would be after the first few months. They carry the baby in the correct position and really cuddle your baby right onto you.
connecta - this is a simple to use buckle carrier, based on the mei tai design but with no long straps to deal with. It's good from newborn and has a fairly long useful life - it can be worn on the front or the back. It's def good until about 12-18 months. After this time, you may be better off getting something a bit more padded and structured and that really moves the weight onto your hips. Some people do use them longer, though. It's great value and is an excellent alternative to all the main 'crotch danglers' out there.
Next up, the more sturdy SSCs - ergo, yamo and manduca.
These are better when the baby is a bit bigger, so lots of people switch to these later on. That said, though, ergo and manduca (I think) do an infant insert which apparently makes them more suited to babies. They still seem a bit big and substantial for little babies to me though. Although these may look more similar to high street carriers, they all hold the baby in the proper seated position and can be used on the front and the back up to pretty hefty weights.
For the keen sling users, there are mei tais and woven wraps - these involve tying knots and things - they aren't difficult but do take a bit of practice - I can link to these too if anyone is interested. Since they involve long straps and knots etc, they are far more adjustable and versatile than any of the other carriers - but they aren't as easy to use.
For general sling info, the slingguide website is really useful.