Can somebody recommend a membrane for removing protein from biological samples being prepared for reverse-phase HPLC, in which the sample is the supernatant from centrifuging a homogenate of bacteria?

We use mostly microcon 30 (30 000 MW cutoff, from amicon-Millipore) or larger volume variations of these centrifuge ultrafilters. For smaller MW, Pall Filtronīs 1K centrifuge filter has been very useful.
You may need a microfilter (0.4... or 0.2... ĩm) ahead of the ultrafilter to prevent plugging, there are devices to do this in one step, donīt recall, offhand, any description. If you donīt find these yourself, send me an e-mail.