I have an Outward Hound Sling that I purchased on EBay, love it - very comfortable for both me and Sophie Kate.
Here is a link to an auction for one.
Outward hound pet dog cat sling carrier tote new - eBay (item 110588655895 end time Sep-23-10 08:22:26 PDT)
If you go to EBay and search on "Outward Hound Sling" you will see all the varietys they have.