I just accidentally found Windows 7’s built in mp3 (and presumably other metadata, exif perhaps) tag editor.
I looked for this thing for what felt like hours over the past year. Eventually I sucked it up and downloaded mp3tag, but its still nice to know that this is there for the next time.
Normally when browsing my mp3 files I see a window that looks like this:
See that summary pane at the bottom? Select a file with editable metadata, like an mp3 and resize that pane. Then click one of the metadata values.
Wow, I wish that had been more discoverable. –1 point for Windows 7 for making that far from intuitive, but 1 point for Windows 7 for having the feature.