I am unsure if I ever decide to do a tool like this. I feel this topic is covered by existing tools and there is not much room for improvement. There are two advanced functions: lossless jpg rotation and automatic rotation by EXIF tag (if you happen to have a camera with orientation sensor). Both of them are available in the current tools.
You can try for example Mike Lee's set of tools: http://phototools.wordpress.com/jpegbox/
RealWorld Photos has an automatic (by EXIF tag) rotation batch operation and droplets can be created for drag and drop style of of processing, but that is not a free app.