I have a stupidly large number of songs in my iTunes library. As I type this, the number of tracks sits at 46,299. Over the years, I've tried many different plugins and programs to make sure everything is as organized, labeled and tagged as possible.
For the past year or so, I've been using a program called TuneUp, which, from what I can tell, is about the best of its kind out there. It cleans tracks reasonably well and finds artwork to almost everything. It's not perfect, but I'm glad I have it.
TuneUp is always being upgraded and improved. The latest iteration (introduced this week) is the feature that displays the lyrics to whatever song you're playing in iTunes. Sure, you could go out and find the words your favourite songs yourself, but why bother? It's actually kinda cool.