OS X's Notification Center was introduced in Mountain Lion and is now your one-stop location for all alerts. Besides the customary notifications for incoming emails and reminders, you can also use Notification Center for other content like the title and artist of the current track that's playing in iTunes.
As showcased by OS X Daily, Now Playing uses AppleScripts and Terminal-Notifier to display the current iTunes track and the artist's name along with your other notifications. The app also works with streaming services like Spotify. Now Playing can be downloaded from Mediafire and installed on your OS X Mountain Lion machine.
Another alternative is iTunification from Onible. Inspired by Now Playing, iTunification lets you display the current track and artist in Notification Center and has the added benefit of Growl support. Besides the track and artist name, the Growl option also allows you to display cover art and setup custom alerts.
Both of these apps are scaled down versions of GrowlTunes which adds playback controls your menu bar and displays the current track and artist as a Growl notification.