As said before, with 480p (720x480), you can get a DAR of 4:3 or 16:9 by applying a SAR of 8:9 or 32:27, respectively.
Furthermore, AFAIK, BluRay doesn't use anamorphic video for the "HD" resolutions (720p and above) at all, so those should all use a SAR of 1:1. Anamorphic video is still used for NTSC (480p) and PAL (576p) - for historical reasons.
For details, please have a look here:
http://www.x264bluray.com/