My leather brush is actually a soft nylon wheel brush. It's sort of shaped like those lug nut brushes.. Either ways it works pretty good. It's soft enough but still has a little bite to it, haven't had to use it much lately as most of the leather I've cleaned lately isn't too dirty and Megs D181 onto a clean terry towel does the job.
If the leather is really dirty I use my little McCulloch steamer.