I was looking around for some batch file renamers, so you can rename multiple files at once very easily, and the three I liked were these:
Some of you may have heard of this. It's GPL'd. It's probably the simpler of the them. It's got an easy way to set many renaming rules, and the interface is pretty easy to grasp. There's some screenshots here to give you a basic idea.
Now, this is also a very good file renamer, but it's got a lot of features, and may be more than a lot of us need, and even too confusing for some. Just take a look at the screenshots here. In the end, it is quite decent, just a lot of ways to set rules, etc.
Multi File Renamer
Now this one's probably the simplest of them. It's easy to set rules. You can set quite a few rules. The interface isn't at all cluttered, and it's easy to select you files. This is what I use personally (sometimes Metamorphose as well). Here's a screenshot of the main interface.
Just to note, I thot that Multi File Renamer used .NET, but I may have confused it with another a tried once. So I don't think it does.
So please let me know which one you think would be best as a portable app.