Hmm..... Well, I quite like alot of the music in this anime. Even though I don't speak much Japanese (At all), I still like some J-pop.. owo
I think my favorite from K-ON! is "Don't say lazy."
I can sing a few lines from the first part, even. XD

Pleases don't say "You Are Lazy."
Datte hontou wa crazy
Hakuchou tachi wa sou~~...

And that's all. XD
Though I'm not very good at singing. owo;

What about you? XD