 If you liked
K-On!
|
 ...then you might like
Mitsuboshi Colors
|
Both series are slice-of-life anime that are pretty comedic. While the girls in Mitsuboshi Colors do not play instruments, they have similar senses of humor and enjoy their life with very little drama.
I would say Mitsuboshi Colors mixes the naughty-children humor from Calvin and Hobbes with the cute, playful attitude of the K-On band members, so if you are also a fan of both I would really recommend this show.
Also, it has a bright color palette similar to K-on, and a similar art style.