UPDATED: This Tag That Tag v4.3

This Tag That Tag will assist with swapping, copying, and appending data between two user-chosen tags in selected tracks or tracks in the selected playlist:

Swap - swap data between tags, ex: ARTIST<->COMPOSER
Copy - copy data from one to another tag, ex: ARTIST->COMPOSER ARTIST
Append - append data from one tag to the end of another, ex: ARTIST->COMPOSER - ARTIST
Prepend - prepend data from one tag to the beginning of another, ex: ARTIST->ARTIST - COMPOSER

This lateset version adds "Date Added" and "Release Date" to the "This" tags. Like the number properties already available, date properties cannot Swap with the text properties available as "That" tags because date properties can't accept text. The dates can be coerced to text in this format: YYYY-MM-DD HH:MM:SS so that they can be sorted properly.

This Tag That Tag is free to try for 10 days, $1.99 thereafter, free for registered users. More info and download is available here.

UPDATED: Artist to Last-First v3.0

As you probably know, the iTunes Sort tags allow you to tailor how a particular tag is, uhm, sorted. For example, an Artist tag may be "Bob Dylan" but you probably don't want your Dylan tracks sorted by "Bob"; entering "Dylan, Bob" in a track's Sort Artist tag will ensure that that track will sort on the last name when sorting by Artist. Or, another common situation is when a band starting with "The", such as "The Allman Brothers", ends up being sorted in the T's rather than the A's. Putting "Allman Brothers" in the Sort Artist tag rectifies that.

Tracks from the iTunes Store almost always have the requisite Sort tags set. But the stuff you rip or import yourself probably won't.

Artist to Last-First v3.0 assists with automating this procedure. It will parse the text of the chosen tag (Artist, Album Artist, Composer or one of their Sort siblings) in a selection of tracks and copy the result to the selected tags.

As you can see from the screenshot, Artist to Last-First doesn't just work with the Artist tag (but for legacy purposes I've kept the script's name as it has been since 2002).

More information and download is here.

UPDATED: Artist to Album Artist v3.0

Artist to Album Artist v3.0 will copy the Artist tag to the Album Artist tag of the selected tracks.

Sorry there's no screenshot but...there's no UI to show. The thing does what it says with little fuss.This latest version is a maintenance update for compatibility with iTunes11+/OS X 10.9+. I find myself needing to use this pretty frequently after ripping CDs or re-adding files.

UPDATED: Filenames to Song Names v3.0

Filenames to Song Names v3.0 will rename the selected tracks in iTunes with their filenames (minus the extension). There is no accounting for prefixed track numbers or other extraneous text; whatever text is in the filename gets pasted to the Name tag as-is.

This update is a maintenance release (last update was in 2011) and is codesigned for your protection.

UPDATED: Multi-Item Edit v4.0

Multi-Item Edit v4.0 allows you to edit most tags (and some additional options) of the selected track(s) in a single always-available floating window using single-edit mode (one selected track) or multi-edit mode, which emulates the pre-iTunes 12 "multiple items" format; that is, a checkbox adjacent to each tag allows you to select which changes are to be applied to the selection's tags.

This version adds Save and Load options so that a configuration of tag and options settings can be stored for later recall and use; adds Information Tracking toggling; adds a "Clear" feature; minor performance fixes.

Multi-Item Edit is free to use full-featured for ten days, $1.99 thereafter. More info and download is here.

Check out the video demo:

NEW: Remove Leading-Trailing Spaces

Remove Leading-Trailing Spaces will remove any number of extra space characters at the beginning and ending of chosen tags (Name, Artist, Album Artist, Album, Composer, Genre, Grouping and Show) in the selected tracks.

Selected tags are remembered between launches.

iTunes 12 won't let you add leading or trailing spaces to a text tag in the Get Info panel so these sorts of anomalies are likely to be the result of tagging by another means (by editing a tag directly in the iTunes browser window, for example, or by using another application).

UPDATED: Sundry Info to Comments v4.0

iTunes knows some stuff about your tracks but won't let you see it other than via the Get Info panel because there are no columns in the browser window to accommodate it. We can fix that.

Sundry Info To Comments v4.0 can copy your single choice of filename, file path (location), file's parent folder path, file creation date (YYYY-MM-DD HH:MM:SS), current playlist, volume adjustment, start time or stop time (HH:MM.SS), artwork size (WxH), purchaser name or purchaser account ID to choice of Category, Comments, Description or Episode ID tag of each selected track. By putting data in one of these available tags it can be visible and sortable or used with Smart Playlist criteria.

Setting up to copy the Apple ID to the Episode ID tag of the track selection.

This latest version adds the track's start time, stop time and artwork size as info to apply; adds the Episode ID tag as a potential target tag; adds user-enterable separator-text field when appending to extant tag text; now stays active and frontmost until Quit; has minor compatibility adjustments for OS X 10.10.

Sundry Info To Comments is for OS X 10.8 and later and is free to use full-featured for ten day, $1.99 thereafter. More info and download is here.