General positive:
* Amazing
* Fantastic
* Excellent
* Splendid
* Terrific
* Brilliant
* Marvelous
* Spectacular
* Super
* Great
* Awesome
* Extraordinary
* Remarkable
* Outstanding
More emotional:
* Delightful
* Charming
* Captivating
* Enchanting
* Beguiling
* Breathtaking
* Exhilarating
* Heavenly
* Blissful
* Euphoric
More formal:
* Magnificent
* Sublime
* Exemplary
* Impeccable
* Superior
* Ideal
More casual:
* Rad
* Cool
* Sweet
* Epic
* Boss
* Killer
* Out of this world
The best synonym for "wonderful" will depend on the specific context and the emotions you want to evoke.