YKK, it you don't blow your brains out from an intolerability to slice of life you should come out happy.
Also, Ai Kora. This idiot doesn't know how to be sad. Please, not these are on opposite ends of the innocence scale for those who would be wary.
After that, I'd say you can never go wrong with Perfect Girl Evolution for a reverse effect on the dark mood. Somehow the main character is so dark that you can't feel depressed because it would be an afront to her level of darkness. Also, it is funny.
As for anime, I'm gonna say Pani Poni Dash is omega happy except for the damn rabbit and old man and certain other characters on occassion, but even when it isn't happy the series isn't serious enough to make you feal the same.