ARen is a lovely little application that did exactly what I wanted it to, and has a variety of other options besides, depending on your renaming requirements. I have no qualms about recommending it very highly indeed.

I rename my digital photos to the date and time that the photo was taken (YYYYMMDD_HHMMSS.jpg) to help me categorize them later. Using the seconds in the filename insures that each filename is unique. I have been searching for months for a renaming utility that will do this, and Aren is the only one that I have found that will do it. It handles all of the standard file renaming duties as well, but this was my primary reason for choosing it.

I rename my digital photos to the date and time that the photo was taken (YYYYMMDD_HHMMSS.jpg) to help me categorize them later. Using the seconds in the filename insures that each filename is unique. I have been searching for months for a renaming utility that will do this, and Aren is the only one that I have found that will do it. It handles all of the standard file renaming duties as well, but this was my primary reason for choosing it.

has some problems with displaying the files but it works... :)