Lightbox XMP provides a way for Aperture users (both 1.5 and 2.0) to export XMP metadata for other programs, such as Adobe Photoshop, to read. For referenced master files, you have the option to just write sidecar files automatically in the same place as your master image. For exported versions, Lightbox XMP also allows you to embed the XMP data into your image.
Lightbox XMP can be purchased for $9.95
