Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
I can think of a few apps that do some of the features

- Global Shortcuts: Quickly control iTunes from anywhere. Play, pause, rate, show, skip, rewind, fast forward .. whatever! CoverSutra gives you total control over your music with customizable keyboard shortcuts.
Quicksilver can do this
- Information Bezel: CoverSutra alerts you of any song change, so you always know what’s playing. Bezels also work nicely with Shortcuts and your Apple Remote: You’ll get Feedback for every single action.
Growl

- Jewel Case: For those who like their artwork on the desktop.
Sizzling keys
 
Coincidentally What psychofreak just listed as alternatives are the ones I use.

However I don't use growl for showing what song's are playing because Sizzling Keys does that for me anyway. I gave Growl's version a go but it didn't show as well. But those three applications together are a brilliant combination. :)
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.