More advanced Smart Playlists, that allow boolean logic.
The ability to edit a track's data in iTunes WITHOUT iTunes writing the new data to the file. I'd rather have it stored in iTunes' own database. It makes backing up a huge pain the way it is, because I there are all these liiittle changes in this biiiig files, so what can I do? Either I back up my entire music collection AGAIN (that's like 10-15 CDs), or I lose all the changed I've made to my metadata. I'd like an option to have it only write metadata to the files when you specifically tell it to. iTunes already stores a lot of metadata in its own database as it is, like play count, rating, etc.
An option to add my OWN tags to files. There are no limits on what tags you can put in an mp3. Give me the ability to make my own tag, and specify its name and data type. And, of course, I'd need to be able to display these custom tags in the main song list and use them in Smart Playlists.
Smarter Party Shuffle, please! Whenever I turn the "play higher rated songs more often" option on, its selection quality goes straight to hell. I get the same track listed 2-5 times in my 15-song playlist! Sheesh! It should have a rule (at least as an option), to never have the same track repeated twice in the same visible list.
I'd also like to be able to re-order randomly-ordered playlists the same way I can in Party Shuffle. There's really no reason this shouldn't be possible. The advent of Party Shuffle made the absence of this feature much, much less annoying, but it still ought to be there.
Fix the weird behavior of dragging the active track in Party Shuffle. As it is, there's NO WAY to move it later in the sequence. If you drag it, it just pushes all the tracks you dragged it over onto the other side! Aaaah! That's totally unintuitive and not helpful at all.
The ability to MANAGE the authorized computers attached to an iTMS account. The whole "be sure to de-authorize your computer before re-initialize your disk" business is bullshit. The only time I reinitialize my disk is when I can't boot, so how the heck am I supposed to de-authorize it?!?!?
I filled up my entire account this way. Sure, you can email Apple Support and get them to fix it (which I did), but why should you need to? You should be able to at least SEE the list of authorized machines, if not edit it manually. I mean, for all I know someone has authorized their machine behind my back.
Options to define how iTunes auto-names/sorts files. I hate the way it does it as it is, so I do all my sorting myself, but that's more of a hassle than it should be, and it's just simpler if the track data and file names are always in sync, which is just too hard to manage manually all the time.
The ability to run visualizers as desktop backgrounds.
I can do it with screensavers (with the help of Backlight 2), so why not iTunes visualizers?