Rating from Playlist.
 

I like the 1-5 star rating system built into the media library. However, I think it would be more convenient if the right-click menu from the Playlist would include the rating. As it stands if there's a lot of music loaded in the playlist, you have to dig around in the library and find the song you're listening to to rate it.

From the Wishlist sticky (read this first)

Media Library: Local Media Views

Ratings accelerator keys or rating from main/playlist windows, etc
Rate It plugin, adds Rate Item to playlist rt-click menu
Toaster plugin, incorporates Rate It, plus hotkey accelerators, and more