don't know what aspect of K-on you like but if it's about a bunch of girls and slice of life / comedy

1. Girl Friend BETA - meaningful show, way many characters, random stories.
2. Lucky Stars - awesome comedy, love their conversation
3. Yuru Yuri - might not be everyone's cup of tea but it's fun (2 seasons for it)
4. A-Channel - yet another one of those friendship shows
5. Toaru Kagaku no Railgun / Toaru Kagaku no Railgun S - ok la this one abit off but I really like them very much, a group of girls (1 main star) - action / adventure.
6. Kiniro Mosaic - haven't finish this but quite fun.

1. Guilty Crown - boy inherits power
2. AccelWorld - digital world combat, where's season 2?!?!?!
3. Kill la Kill - over the top awesome stuff
4. Tengen Toppa Gurren Lagann - over the top awesome stuff ........... many years before Kill La Kill