I've been looking at slings too - thinking about a hotslings sling. I've found lots on ebay, and they have some pretty cute patterns.
For long-term carrying CalebsMum, especially for a bad back, I'd suggest something with a bit more total back support. I'm planning to use my sling for quick carrys - popping in at the grocery store, or whatever. For longer wearing, I still use my moby wrap, and find it very comfortable and supportive. Great for a newborn too - DD would sleep instantly in it! It's similar to a hug-a-bub, but without the pocket, and half the price! (google it, if you're curious) The down side, is that it takes a minute to put on, which is why I'm looking for a sling as well, but, as I said, if you are going to be wearing your baby for more than a few minutes, I'd say it's worth it!