EasyTag (v. 2.1.6)
EasyTag is a tagging application that can handle more than just ID3 tags. Files that EasyTag supports include MP2, MP3, MP4, OGG, FLAC, AAC, Monkey's Audio, MusePack, and WavPack. Bulk rename, playlist creation, and directory rename/restructure are some of the other features found in EasyTag.
Under the menu bar sits the main toolbar, which holds key functions like next/prev, first, last, undo/redo, scan, remove tag, save, file tree/list view switcher, select all, invert selection, search, CDDB lookup, create playlist, stop, and quit. Below the toolbar is an input box to select the parent directory. The bulk of the application window is split into three vertical panes: file tree/list view, files in the current directory, and the tag editor. Under the three panes is an activity log and status bar.
EasyTag does pretty much any tagging operation you can imagine. The most notable features are undo/redo, CDDB lookup, and the variety of supported file formats.
Kid3 (v. 1.4)
Kid3 is an audio file tagger for KDE 4.x. Supported files include MP2, MP3, MP4, OGG, FLAC, WMA, WAV, AAC, AIFF, WavPack, MPC, Speex, and TrueAudio. Tags can be created automatically from file names or the other way around. File names can be changed using 20 different combinations of title, artist, album, track number, and year. Playlist creation and directory editing are also included with Kid3. There are nearly 60 different tag categories available to edit in this application.
As a KDE 4.x app, Kid3 looks great, with highly configurable toolbars that suit anyone. Logical placement of essential elements makes Kid3 complete, without hiding functions within menus or cluttering the UI. This is probably the best choice for users of KDE, and the support for every desktop platform is nice for OS-hoppers. If CDDB lookup was included, Kid3 could be the best tagger out there.
MusicBrainz-Picard (v. 0.12.1)
MusicBrainz-Picard is the official tagger application of the online community-based MusicBrainz database of metadata, with the Picard coming from the famous captain of the USS Enterprise D and E. This application supports most audio file formats. Picard utilizes MusicBrainz for album cover, as well as CD and digital audio file tag lookup, though the file names can also be used to populate that info. Picard can also rename or move files to other directories and create new folders.
The user interface is clean and all elements are well-placed. Directly under the menu bar, you'll find the main toolbar, which houses every essential function from the menu bar The bulk of the window is split between two panes; the left holds files added to Picard with current tag info, while the right contains the new file names and tag data. An optional file tree browser pane can be enabled via the View menu.
Entagged (v. 0.35)
Entagged is a Java-based audio file tagger for MP3, OGG, and WMA files. Other options include file renaming, directory editing, playlist creation, and lookup via freedb. Files can be renamed based on the tag information, or vice versa (tagged based on filenames).
As a Java-based application, Entagged is not the prettiest thing in the world. The UI is composed of different shades of yellow and every on-screen element is made of blocks (there are no rounded corners to be found).
Sorting options are good, though. Audio files in the current directory can be sorted by file name, artist, album, track number, title, length, and genre. Other draws of Entagged are support for WMA files and the availability of a Windows-based version.
Ex Falso (v. 2.2.1)
Ex Falso is the audio file tagger included with the Quod Libet player application, though it can be obtained independently via the Ubuntu Software Center.
Supported files include anything that Quod Libet can play: MP3, OGG, FLAC, Musepack, and MOD. Ex Falso allows for manual tagging of individual songs or in bulk using the file name as a template. Bulk rename is also possible, as well as album-based track numbering (for instance, 1/12, 3/12).
The user interface is very simple, with no menu bar or toolbars. The left-hand pane holds a file tree for folder selection above the list of files in the currently selected directory. The right-hand pane, where the actual work happens, is tabbed to switch between the manual tag edit, tag from file name, rename, and track number editors.
K-Yamo (v. 0.40a4)
K-Yamo stands for KDE--Yet Another Music Organizer. This application edits tags for MP3 and OGG files, but also includes a CD ripper. The CD Ripper can utilize freedb to auto-populate tags and file names for ripped tracks, and MusicBrainz support can fetch tags for files not ripped by K-Yamo.
The KDE 3.x-style UI is extremely efficient. With no menu bar or toolbars, K-Yamo makes use of tabs to switch the main window between tagger, ripper, settings, and the about screen.
K-Yamo is a very basic application for tagging audio files, with no directory creation/renaming, sparse file type support, and only the most basic tags. The included CD ripper and overall simplicity are its strong points.
Audio Tag Tool (v. 0.12.3)
Audio Tag Tool can edit ID3 tag information of MP3 and OGG files. Tags can be edited individually or in bulk, either manually or using the existing file name. Default fields include title, artist, album, year, genre, comments, and track number.
Switching to the advanced view allows for the inclusion of contact, copyright, date, description, isrc, license, location, organization, performer, and version. Bulk rename and and a playlist creator round out Audio Tag Tool's capabilities.
The user interface is simple enough (even in advanced view) for anyone to pick up and use. Split in half vertically, the left pane is home to the file list of the current directory. The right pane is tabbed to switch between single-tag edit, multiple-tag edit, tag clear, bulk rename, and playlist creation functions.
Audio Tag tool is a good tagging application, and there is a .deb for ARM available if you're already living in the future.