I'm about to fully endorse

http://www.irfanview.com/   ||||||It's fo' free!||||||

I've been using this for seems like forever for just basic photo editing and viewing and I just now found out that it batch renames photos! It's the best thing I've discovered all year. I'm trying to organize all my shit so I can find things without having to go one by one and I was thinking I would have to download a whole new program and learn how to use it to batch rename. Turns out I already had what I needed all along.
This site is what I used to figure out how to rename through Irfanview.

I have to admit though, I hate the name of this stupid program because I always misspell it on the first try.