YAGP is the one stop shop for geotagging image files on Mac OS X. Without leaving this app, you can find locations and modify metadata in the images. YAGP uses ExifTool to modify metadata. And it provides three ways to specify locations, clicking on map, searching an address and manually entering.
YAGP is hosted by SourceForge under GPL license. Currently it is feature complete. The alpha release will be available soon. Meanwhile, anyone can access svn repository using "svn co https://yagp.svn.sourceforge.net/svnroot/yagp yagp".