Here are a few useful software products

Bulk Rename Utility
A great tool to bulk replace foreign characters that can break various plugins and music players.

"Bulk Rename Utility is a utility which allows you to easily rename files and directories, based upon extemely flexible criteria. Add date-stamps, replace numbers, insert strings, convert case, add auto-numbers, process folders and subfolders....plus loads more!"

mp3Tag
A great mp3 tagging tool, can also tag FLAC files and embed album art.

dBpoweramp
A nice ripping tool that will automatically populate the tags, add Replaygain and album art as it rips your CDs.  Supports secure ripping to loads of different formats, mp3, flac etc.  Only downside with this application is that its subscription based so expires!

DiffMerge
A great free tool for comparing differences between text files for Windows, Linux and Mac OS.

Helpful for when you made a change to a plugin a while ago and cant remember now what you did