Not sure if this is so much an affiliate tool, but it's certainly a great help in building my websites. I've been putting up a LOAD of pictures (1400 ish) on one of my sites and have used Webmerge to build the pages, so I made my own datafeed to plug into Webmerge. This:

http://www.bulkrenameutility.co.uk/Main_Intro.php

has been a fantastic help saving me literally hours and hours of effort. It's one of those dull-but-worthy tools that once you realise how useful it is, you can think of more and more things to do with it.

It's free, but there's a PayPal donation link. I first used it a few months ago and rediscovered it today when it turns out that the latest version allows me to do exactly what my latest problem was - I gladly gave the guy $20 for his efforts.