Bulk File Rename Utility is a wonderful app that let's you quickly rename lots of files in great ways. Here are some of those ways:
Adding an ISO-8601 date before each file name. ISO dates always sort correctly. Here's how you can add an ISO date prefix:
Select your files, hit Rename and boom, you've got ISO dates on all your files. The result will look something like this:
2015-07-31 - filename.txt
Pretty nifty!