| Magento is the newish cart app that developers seem to be jumping on the bandwagon lately. It's extremely robust and as a result requires very specific server tweaks and good hardware or else it will run slowly. However if it wasn't so huge and demanding it wouldn't be so damn powerful. Magento does allow you to make users who only have access to a specific part such as the catalog section of the backend which is where all the product info is created and edited. But it will also give them access to other vendor products. Who knows there might be a hack that could do what you want it to. Might want to search their forums. It is open source and the community version is free. The enterprise version is for large retailers/corporations which I don't think you will need.
If you do decide to go with Magento I would recommend you go with a dedicated Magento host. It's pain to set up with ftp and like I mentioned before some tweaks have to be done server side so you are going to be in contact with your server admin.
If you want to set it up on your localhost to try out and need some help feel free to pm me here. | 