Any medical image viewer that uses DICOM to access images should be able to integrate with dcm4chee.  This includes commercial as well as open source applications.

• If you're using a Mac, you really can't go wrong with the open source Osirix application.  It is an extremely sophisticated, full featured application for viewing and manipulating medical images.
• Merge eFilm has been a work horse in the stand-alone viewer market for years.  Too bad it isn't free anymore!