Formal:
* Beatitude: A state of perfect happiness or blessedness.
* Ecstasy: An overwhelming feeling of great happiness or excitement.
* Euphoria: A feeling of intense happiness and excitement.
* Rapture: A state of intense joy or pleasure.
Informal:
* Joy: A feeling of great happiness and contentment.
* Delight: A feeling of great pleasure.
* Contentment: A state of happiness and satisfaction.
* Serenity: A state of peace and tranquility.
* Heaven: A state of perfect happiness and peace.
Poetic:
* Elysium: A place or state of perfect happiness.
* Nirvana: A state of perfect peace and enlightenment.
* Paradise: A place or state of perfect happiness.
The best word to use will depend on the context and the specific feeling you want to express.