My minimalistic solution involves using GeekTool to display a geeklet like the one I made on top of the menu bar. It runs an AppleScript every 10 seconds and will unobtrusively display nothing when iTunes is not running or not playing, otherwise just show the current track's name.
Advantages: you can resize, position and format the text of the geeklet as you wish (e.g. put it in the very center of the menu bar – something the freeware programs discussed here can't do), as well as have it display additional info such as album, artist, etc. by editing the AppleScript. See here for ideas.
Disadvantages: The geeklet's position is fixed. When your front application uses a lot of space on the left-hand side of the menu bar, the geeklet will be shown on top of the rightmost menu items. This problem is, of course, more relevant for small display sizes.