Aperture 3 could be used for batch conversion. You import the RAW pictures into a library. When importing you could have a set of pre-defined settings. Choose
Import Settings -> Adjusment Preset. Select the preset you like. If there is no one that you like, you could edit/create your own preset. During the import process it is also possible to do a backup of your files, which I think is handy. Of course you could do simple things like renaming pictures etc. When you have them all imported, you could export them at once or apply your adjustment.
The process is semi-automatic, you will have to select the settings before import and the choose your settings when exporting. If you want to automate everything, I suggest using the
Automator application that is provided with Mac OS X.
I use Aperture 3 for batch processing and a like a lot. It is cheaper than PhotoShop. It is available for Mac OS X.