It's no embarrassment to confess that K-ON!! ep20 just made me cry. The way they talked after the live show was so touching, and the actors played it really nicely. It also sort of reminds me of the days when I played with my friends at schools and a college.
K-ON! in general is just a good comedy with cute girls, sometimes playing music (but not always). Kyo-ani has proven that they can make a really touching episode out of it, like they did with Lucky Star ep22.