Namexif™ is a tool to automatically rename photos with the date they were shot.
Digital cameras have their own clock and record the date to each photos with a precision of a second. Since the date and time is recorded for each photos (provided it is an EXIF compliant digital camera), Namexif™ is able to rename these photos according to the date.
Doing so will:
make chronological order same as alphabetical one,
set a unique name to your photos
http://www.Digital Camerasoft.com/softnamexif.html

Have not tried, but seems good, also has the option to save the original file name at the end of the new file name

best bit is it's free!