Actually Photoshop (32 bit, up to CS5 at least) can still open PCD files
upon carrying over the Photo CD.8BI plug-in from an earlier Photoshop version and placing it in the Plug-ins/ File Formats folder.
Not sure about the last Photoshop version that shipped with the plug-in, maybe CS2. Hope it is ok to attach it here. Windows only.
Otherwise the pcdtojpeg
command line utility by Sandy McGuffog works well,
output is limited to sRGB 8 bit JPG though.