Sometimes, Photoshop files (PSD) do not show up in the Import window in Aperture.
This happens if there is a TIFF file with the same name at the same location; only the TIFF file will appear. One way to work around this issue is to simply drag the PSD file directly onto a project icon in the Project pane. Alternatively, you could rename one of the files before importing.
This document will be updated as more information becomes available.