Do a Google search for free xyplorer and you'll get this page or just go here to get the free version.
It's version 5.5........<a href="http://www.xyplorer.com/free.php">xyplorer</a>

My favorite file re-namer.  It's got to be File Re namer Basic.  Get it at <a href="http://www.sherrodcomputers.com/products_filerenamer.cfm">File Re namer Basic</a>

It's got ton's of features like a explorer interface, and fast scanning of folders.  It finds the files for you all you have to do is click on a folder and scan.  Files are displayed in the right pane.

My favorite feature is the ability to select just the files you want to rename,with just a click of a button.  You can select all files in a folder or just a few. 

Other features include list or thumbnail view.  Can add a prefix or suffix, custom file extension and numbering.  It also has a file history option and a undo feature.

Here's a screen shot