General happiness:
* Joyful
* Cheerful
* Delighted
* Glad
* Pleased
* Content
* Elated
* Euphoric
* Jubilant
* Thrilled
More specific synonyms:
* Peaceful: Feeling calm and tranquil.
* Excited: Feeling energized and enthusiastic.
* Fulfilled: Feeling satisfied and complete.
* Content: Feeling satisfied and at ease.
* Blissful: Feeling extreme happiness and joy.
* Exuberant: Feeling full of life and energy.
* Giddy: Feeling lighthearted and carefree.
* Merry: Feeling joyful and festive.
Informal synonyms:
* Tickled pink: Feeling very pleased.
* Over the moon: Feeling extremely happy.
* On cloud nine: Feeling very happy and carefree.
The best synonym for "happy" will depend on the specific context and the feeling you want to express.