Skinitunes is a free mini-player that runs alongside the massive iTunes. It consists of two different iterations: the Mini Player, which is a small rectangular app that has standard media player controls on it, and the Skini Player, which is an extremely small horizontal bar that sits at the top of the screen. Skinitunes can switch back and forth between the two players in the middle of a track, but can't minimize completely.
iTunes already has a built-in mini player, but this is a nice alternative as it shows the album artwork, has an optional short-lived popup box when a new song starts, and has optional skins for itself. The skins for SkiniTunes change its appearance to one of several graphical variations.
SkiniTunes 1.0.5 works flawlessly with the most recent 184.108.40.206 version of iTunes, and it uses between 4 and 6 megabytes of RAM, about ten percent of what iTunes will be using at any given time. It also doesn't use up much CPU, which is good, because iTunes itself is a memory and CPU hog as well as a screen hog.
SkiniTunes is completely free, but there are numerous grayed-out features that are only available in the $5 SkiniTunes Pro. Pay-only features include downloadable lyrics, app transparency effects, and the ability to use hotkeys in general and from within any application to control SkiniTunes. These features are nice, but certainly aren't required to enjoy the SkiniTunes experience.
One feature that'd be nice in a future version is integration with the iTunes Genius feature. Genius constructs a short playlist based around the type of music that's currently playing. It'd be handy if SkiniTunes had a Genius icon that would tell iTunes to make such a playlist. As it is, you can see iTunes' existing Genius playlist from within SkiniTunes, which will have to be good enough.
Since iTunes' own mini player is kind of blah and isn't really standalone from the iTunes software itself (it goes away every time you try to do something in iTunes), having a dedicated player that can access iTunes music is pretty neat.
Note: SkiniTunes is free. There's also a fuller-featured SkiniTunes Pro, which is $5 and adds lyric and hotkey support. Due to an unusual installer setup (.msi inside an .exe), some antivirus programs register a false positive for this file.