Panda Batch File Renamer is a handy tool that will quickly rename tens, hundreds, maybe thousands of files according to the rules that you define. (Despite the name, it has no connection to Panda Security.)
At its simplest you might want to change the case of a file name, replace some text with another, or remove particular text altogether.
The program can also insert new text, though, and this can be extracted from metadata within the file itself. So you could create a set of rules that, say, renamed your MP3 files to include the track, album and artist (and genre, track number or year), while photos can be renamed to include their subject and dimensions.
Of course these options will only work if your files have the appropriate tags and metadata, but Batch File Renamer does have some simpler options that will work on just about anything. So you can add the height and width to most image names, for instance, while files in general can be renamed according to their extension or parent folder name.
You may have to create several rules to create the names that you want, and the results of all this could be confusing. In a thoughtful touch, though, Panda Batch File Renamer displays the "before" and "after" file names on screen as you work. These are updated as soon as you make any changes, and so you can preview what the program is going to do before you click the Rename button. (Although, don't worry - if you forget, an Undo button will quickly restore your original file names.)