AudioRanger is a powerful and versatile music tagger designed to automatically identify and organize your digital music collection.
Runs on Windows and Mac. Feature-rich free version available. (Has limits)

Adds and fixes music metadata and adds album art.
This component displays several groups of items which are described in the following sections. The item names are displayed in upper-case letters in the UI element, but can also be used in lower-case in title formatting code, since field names in title formatting are case-insensitive.
This is Michael Mutschler’s famous mp3 shell extension, also available for Windows 7 and 64 bit.
MediaInfo is a convenient unified display of the most relevant technical and tag data for video and audio files.
MusicBrainz is an open music encyclopedia that collects music metadata and makes it available to the public.
MusicBrainz aims to be:
- The ultimate source of music information by allowing anyone to contribute and releasing the data under open licenses.
- The universal lingua franca for music by providing a reliable and unambiguous form of music identification, enabling both people and machines to have meaningful conversations about music.
- Like Wikipedia, MusicBrainz is maintained by a global community of users and we want everyone — including you — to participate and contribute.
musicbrainz.org
musicbrainz.org/doc/General_FAQ
wiki.musicbrainz.org/External_Resources
community.metabrainz.org
en.wikipedia.org/wiki/MusicBrainz
picard.musicbrainz.org
www.foobar2000.org/components/view/foo_musicbrainz