If you're looking for anime similar to K-On!!, you might like these titles. All recommendations are made by Anime-Planet users like you!
Kyousuke Kosaka is a normal teenager with average grades and an average home life, but when he finds out that his overachieving younger sister Kirino has been hiding her vast anime and eroge collection from their unassuming parents, his world turns inside out! Now, having promised to help his formerly distant sibling navigate her two distinct lives, Kyousuke finds himself drawn into Kirino's world of magical girl anime and "little sister" fetish games while covering for his sibling to her parents and friends, not to mention trying to provide what guidance he can.
the character designs are flawless. both these animes are incredibly moe moe moe!!! both of these animes will make you laugh so hard. there are absolutely no corner cuts on the production. they are fully animated and rarely you will see a still picture. watch them for the comedy and character design. if you liked this, you will definitely enjoy the other.
Super Sonico is an 18-year old college student who plays guitar for the three-girl band Fastest Speed in Space and models for pin-ups. In spite of her busy schedule, she still finds time to help her grandmother at her restaurant. One night, her band members Suzu and Fuuri, are late to a concert, forcing her to play alone. The result of that show will have far-reaching consequences for Sonico.
Both anime feature a lot of young women playing instruments and a whole lot of focus on slice of life stuff (keep in mind that SoniAni is far more vapid than K-On! ever manages to be). SoniAni is very much ecchi, while K-On! usually manages to not sink to such low tactics. The cast in K-On! is much more varied and features several mains, while SoniAni is basically just about Sonico. Still, if you saw one and want more female characters playing instruments now and then, do check the other one out.
As K-on is based upon "cute girls doing cute things", Sakigake!! Otoko Juku is all about "manly characters doing manly things". The reason why you should try both, it's because both these anime make fun of the cliches and tropes of their respective genres and formula in a quite clever way. Notwithstanding that, both of them (despite being polar opposites in almost every other aspect) focus the story on the bound of friendship that the characters develop during their high school days.