For several years I have been using a FREE batch/auto crop tool called JPEGCrops. I recently discovered it has a 4:3 selection.
The review by about.com can be found at http://graphicssoft.about.com/cs/imagep ... gcrops.htm The review is for version 0.6.5 beta (Nov 03) I’m using version 0.6.22 (March 05) The current download version is 0.7.4 (March 07) and can be downloaded from their web site at http://ekot.dk/programmer/JPEGCrops/
(If you do a Google search be aware that this program is jpegcrops. With an s, the other is jpgecrop which I don’t understand at all)
The only drawback I have found is that it supports only jpg photos.
Users can make 4:3 the default crop by choosing File>Preferences>Basic > then select 4:3 in the Default Aspect check box.