ExifExtreme displays all EXIF and IPTC info for an image of almost any type (JPG, TIF, NEF, CR2, ORF, DNG, PSD, etc.).
ExifExtreme is for viewing metadata only; there's no editing capability.
Just drag a file from the Finder to the window, or use File-Open. You can also drag a file to the ExifExtreme icon in the dock. You can have as many windows open as you like--handy for comparing EXIF and IPTC info.