I finished the Anime K-On! about a week ago. I have to say, it's definitely one of my top three favorites right now. Sure, I haven't seen that much Anime, but all the same... this was just wonderful.
I'm not going to give a synopsis right now, but I will say what I loved about this anime so much. It's the friendship and bonding between the girls of the Light Music Club (which is what K-On means, if I'm not mistaken). In fact, this picture pretty much sums it up:
If you haven't already, give it a watch. It's definitely worth your time.