I had remarked a while back that I know of no publisher making their ONIX records available. I've since received two comments pointing out that some records are available. The Cambridge University Press makes them available, along with much other useful information, in their DataShop. The University of California Press has also made ONIX data available. Roy Tennant mentions in his comment he has started collecting publishers freely offering their ONIX data to the public. Such a list could be a valuable resource. This is a metadata standard we had better watch.