nconvert is a fantastic tool to convert and manipulate images. It is available for a huge number of platforms in cluding Mac OS X and some plaforms I thought were long gone :)
To wipe all metadata you have to use the rmeta option, as in:
nconvert -rmeta DSCN0001.JPG
There is a small catch with all such operations depending on your camera. When you take photos in portrait orientation (the long side being vertical), some cameras create a JPEG with the rotated dimensions and others simply flag the jpeg as being rotated. In the latter case, removing all metadata will make all images appear in landscape orientation. nconvert provides an easy fix for this:
nconvert -jpegtrans exif DSCN0001.JPG
...which you have to do before removing the metadata but you can combine into one operation as in:
nconvert -jpegtrans exif -rmeta DSCN0001.JPG
PS: If you use Lightroom to export your images before publication and enable the option Minimize embdeded metadata, your images will be correctly oriented and stripped of metadata except for copyright information which is something you may want to keep embedded anyways.
jhead, which can do coarse-grained removal of all metadata and which works on many operating systems.
jhead -purejpgwill delete all metadata, by the way.