There are TONS of babywearing options, of which slings are just one…
Wraps & SPOC (Simple Pieces of Cloth):
These are of similar design (a giant rectangle of cloth), but depending on the size, and be used differently…really, all babywearing can be said to be a variation of an SPOC that had a strap added here, or a whatever sewen there, size changed, etc…
A wrap is a giant SPOC, while smaller SPOC can be used as a sling…different cultures have tons of names for SPOC’s that are often used for babywearing (generally babywearing SPOC are SPOC that are normally worn as a regular item of clothing from Mexican rebozos to African khangas)
Wrap:
Wraps (sometimes called “wraparounds” or “wraparound slings”) are lengths of fabric (usually between 2 metres and 6 metres, or 2.5-7 yards long, and 15-30 inches wide), which are wrapped around both the baby and the wearer and then tied. There are many different carrying positions possible with a wrap, depending on the length of the fabric. A baby or toddler can be carried on the wearer’s front, back or hip. With shorter wraps it is possible to do a one-shouldered carry, similar to those done with a pouch or a ring sling, although most carries involve the fabric going over both shoulders of the wearer and often around the waist to offer maximum support. These slings are the most versatile, but have a longer learning curve.from wikipedia
Dimensions: ~20 inches long and 12 feet long
MANY MANY ways to use a wrap @ http://gypsymama.com/booklet.pdf
Pareo:
Dimensions: At least 45 inches wide, and at least 45 inches long.
How to use a pareo @ http://www.mamatoto.org/Default.aspx?tabid=84
Rebozo/Shawl:
Dimensions: ~30 in wide and 6 ft long
How to use @ http://www.mamatoto.org/default.aspx?tabID=86
Khanga:
Dimensions: ~ 5 feet by 3 feet
How to use @ http://site.peppermint.com/kikoyInst.htm
Slings:
Adjustable Slings:
These are baby carriers that use dynamic tension, a length of cloth and metal (such as aluminum) or nylon rings. One end of the cloth is sewn to two rings. The cloth wraps around the wearer’s body from shoulder to opposite hip and back up to the shoulder, and the end is threaded through the rings to create a buckle effect. The baby sits or lies in the resulting pocket. Once a sling is threaded, it can be taken off and put back on without rethreading. A threaded sling forms a loop of cloth. The wearer can put one arm and the head through the loop of cloth to put the sling back on.When the baby is in the carrier, the baby’s weight puts tension on the fabric, and the combination of fabric tension, friction of fabric surfaces against each other and the rings combine to “lock” the sling in position. This type of sling can adjust to different wearers’ sizes and accommodate different wearing positions easily: the wearer supports the baby’s weight with one hand and uses the other hand to pull more fabric through the rings to tighten or loosen the sling.
from wikipedia
How to wear @ http://m134.bravepages.com/kel/slinguse.html
How to make @ http://www.mayawrap.com/n_sewsling.php
Fixed/Pouch Slings:
Sometimes called “tube”, “pocket” or “ringless” slings, these are generally formed by a wide piece of fabric sewn into a tubular shape. Simple, or fitted pouches do not have rings or other hardware. Adjustable pouches may adjust with a wide variety of methods, including zippers, snaps, buckles, clips, rings (these are usually considered hybrids), drawstrings or velcro. Most pouches have a curve sewn in to shape the cloth to the parent’s body and hold the baby more securely than a simple straight tube. The wearer slips the pouch over the head and one shoulder, sash-style, creating a pocket or seat to hold baby in. The learning curve is short; most people find that they can learn to use the pouch quickly.A properly-fit pouch can be used to safely wear a baby from birth to toddlerhood. Pouches are ideal for situations in which babies are frequently being removed from the pouch and put back in, for older children who do not want to be carried long but are heavy enough to be difficult to carry in-arms, and for young, small babies who are not heavy.
As with most one-shouldered slings, pouches are not ideal for long wearing of heavy babies, as the asymmetrical weight distribution can create back pain for the parent. The better a pouch fits, the more evenly it is spread across the shoulder and back, and the more suitable the fabric, the better a pouch will be for longer periods of use or heavier children. Proper fit generally means that baby is not sagging away from the parent’s body, is not lower than the parent’s waist or hip, and is not held uncomfortably tight.
from wikipedia
How to make @ http://www.ida.net/users/stace/sling.html
Asian inspired carriers:
Mei tai:
Traditionally, the Chinese mei tai was a square or nearly square piece of cloth with parallel unpadded straps emerging from the sides of each corner. It was tradtionally secured by bringing all the straps together in a twist with the ends tucked. The mei tai did not become well-known in the United States until 2003, when several designs that added padding, a longer body, longer top straps and a more “wrap like” tying method were created and made popular. A variation on the traditional mei tai was popularized in Australia in the 1960s. There are now hundreds of different brands of mei tai available with a variety of features, but the longer straps, taller body and wrap-style tying method are found in almost all of them. Mei tais are suitable for front or back carries with children ranging from birth to as heavy as a parent can support (usually between 35 and 45 pounds is the upper limit of comfortable wearing, but in emergencies and demonstrations, small adults have been worn. Wraps can be used through the same weight ranges.)from wikipedia
How to wear @ http://www.meitaibaby.com/howtoslideshow.html
How to make @ http://www.bradley-etheridge.com/MaeMeiTai.htm
Podegi & Hmong Carriers:
I’m putting these together since they are both single strap carriers…the podegi is a Korean carrier with a large panel (“body”) sewn to the strap while the Hmong carrier has a narrower body and is native to the Hmong.
How to wear the podegi @ http://www.wearsthebaby.com/babywearing/podegi.html
Podegi variations @ http://site.peppermint.com/podegicarry.htm
Hmong carrier @ http://www.freehandbaby.com/hmong-baby-carrier.php
Onbuhimo:
To me, the onbuhimo seems like a sort of Podegi/Mei tai hybrid…it is a carrier that originated in Japan (according to wicipedia, during the 1940’s). It is like a podegi with only one strap, but it has far less cloth like the mei tai…it also has rings that the strap fastens thru and it seems like it is worn more like a mei tai.
How to wear @ http://www.freehandbaby.com/onbuhimo-instructions.php
Out of these, I have tried wraps (IMO, too hot, too bulky and Sophie didn’t like it—it was summer and we both sweated miserably, but others seem to love them), adjustable slings (which can be used for different sized people, minimizing the number of slings you need) and non-adjustable pouch slings (my favorite, and fit to fit me and proly the easiest to learn to use as a beginner)…
Recently I have ordered a Mei tai, since Sophie likes riding on my back, which I think might be easier the more preggo I get, and the heavier she gets (she’s @ 20 lbs right now, and still ok in the sling, but only on shorter jaunts now)…
AWESOME resource for babywearing…http://www.thebabywearer.com/
*all the wikipedia quotes came from http://en.wikipedia.org/wiki/Baby_sling
bay witch musings 
I used gypsemama wraps for my twins. LOVED IT. Since they are so well made I have also lent them to other moms as well. they are on their third baby.