AppleScript
Show the iTunes Library Old School
I'm not certain if this has been mentioned anywhere--I haven't seen it--but I found the defaults command for displaying the entire iTunes library. Remember when you actually had a large playlist named "Library", before Apple split it up into--what I call--"Master" libraries of "Music", "Movies", "Podcasts", and so on? The "Library" listed everything in your iTunes library. Well, you can get that back using this command in Terminal:
defaults write com.apple.iTunes show-library-playlist -bool TRUE
Quit iTunes before entering the command. When you restart you'll have a new playlist named "Library" at the top of your Source list, above "Music".

If you want to remove the "Library" again, use this command in Terminal:
defaults write com.apple.iTunes show-library-playlist -bool FALSE
There is a second preference called "hide-library-playlist", which I at first thought would have to be set in tandem with the opposite of "show-library-playlist", but this doesn't seem necessary. In fact, you can set one or the other, apparently, and get the desired result; that is setting "show-library-playlist" to TRUE or setting "hide-library-playlist" to FALSE amounts to the same thing. Also, for AppleScript purposes, this playlist can be referenced as library playlist 1; it always could be, but now it is visible.
Native Half-Star Ratings
This hint at Mac OS X Hints describes a simple terminal defaults command that allows iTunes to accept half-star ratings by drag or inter-star-clicking.
UPDATED: Add from eMusic Downloads Folder v1.1
Add from eMusic Downloads Folder v1.1 (like Add from Amazon MP3 Folder) will display the Album folders in your designated eMusic downloads folder so you can select which of them to add to iTunes. Optionally, if you allow iTunes to "Copy files to iTunes Music folder when adding to library", you can choose to move the original folder and files out of the eMusic download folder and to the Trash. Latest version runs as application to avoid a potential startup error.
UPDATED: Add from Amazon MP3 Folder v1.1
Add from Amazon MP3 Folder v1.1 will display the Album folders in your designated "Amazon MP3" downloads folder so you can select which of them to add to iTunes. Optionally, if you allow iTunes to "Copy files to iTunes Music folder when adding to library", you can choose to move the original folder and files out of the "Amazon MP3" download folder and to the Trash. Saves a few keystrokes. This newest version runs as an application since the compiled version would often generate an error at startup.
Although the Amazon MP3 Downloader application has a preference to add downloaded purchases to iTunes, I could never get it to work.
NEW: Search Amazon UK MP3
Search Amazon UK MP3 uses terms from the selected iTunes track as the basis for a search of the Amazon UK's MP3 site.
NEW: Reset Tracks Start-Stop
Reset Tracks Start-Stop will reset the Start and (optionally) the Stop Time of the selected tracks--or all the tracks of the selected playlist--to "0:00" and (optionally) their entire duration, respectively. (Erg, that could have been written better.)
UPDATED: Reset Bookmarks to Start v2.0
(Formerly "Reset Bookmarks".) Reset Bookmarks to Start will reset the bookmark of each selected track to its Start Time, effectively clearing the bookmark from its position later in the track. Tracks which have been set to "remember playback position" or which are "M4B" types will have a bookmark position.
UPDATED: Gather Up the One-Hits v2.2
Gather Up the One-Hits had a persistent problem for some users whereby only a single track would be copied to the "One Hits" playlist. I believe I have fixed the problem, albeit at a cost of some speed; but it should only take a few seconds rather than a few moments to run.
Another Reprieve
Dan Frakes emailed me with a vote for maintaining Set Video Kind of Selected:
"One that I'd like to see kept alive, so to speak, in some
fashion is Set Video Kind of Selected. Although iTunes 8 does let you
bulk-edit many of these fields, Set Video Kind of Selected has one unique feature that's very
useful: sequential episode numbering."
I had forgotten about that feature. Make Video Tags also has sequential track, episode ID, and episode numbering.
