Cathodemer [Steam]: Make crazy visuals with sine wave shenanigans, has a ton of fun tools to mess with, there's like twenty million options in here. Would be great for live set visuals if I ever made music. I mostly use it just to generate different flavors and shapes of static to texture videos or make backgrounds. Probably the best $25 I've spent in a long time. Very flashy, so be advised, hitting Randomize might hit you with some seizure lightning.
WizTree: Visualizes space on your hard drives as big colorful blocks, so you can see if there's anything taking up more space than it's worth.
MP3Tag: There might be better software out there for doing this kind of mass music metadata fixing, but I haven't bothered looking, this just does the job.