Strong Emotion:
* Ecstatic: Overwhelmed with joy and excitement
* Elated: Filled with joy and pride
* Jubilant: Feeling or expressing great joy
* Thrilled: Feeling intense excitement and pleasure
* Rapturous: Feeling or expressing great delight
* Enraptured: Filled with intense pleasure or delight
* Overjoyed: Extremely happy and delighted
* Blissful: Feeling perfect happiness
* Exultant: Feeling or expressing triumphant joy
* Delighted: Very pleased and happy
More Subtle:
* Content: Satisfied and happy
* Cheerful: Happy and optimistic
* Joyful: Feeling or showing great happiness
* Pleased: Feeling happy and satisfied
* Gratified: Feeling pleased and satisfied
* Contented: Feeling happy and at ease
Informal:
* Tickled pink: Extremely pleased and delighted
* Over the moon: Extremely happy
* In seventh heaven: Extremely happy
* On cloud nine: Extremely happy
The best synonym for "very happy" will depend on the specific context and the level of intensity you want to convey.