Formal:
* Superb: A bit more emphatic than "excellent."
* Outstanding: Indicates something stands out from the rest.
* Magnificent: Implies grandeur and impressive beauty.
* Splendid: Expresses brilliance and impressiveness.
* Remarkable: Highlights the unusual and noteworthy quality.
* Exceptional: Points out something extraordinary.
* First-rate: Indicates the highest quality.
* Prime: Suggests peak quality and condition.
Informal:
* Great: A very common and versatile synonym.
* Wonderful: Expresses delight and pleasure.
* Terrific: Used to emphasize excitement and enthusiasm.
* Fantastic: Similar to "terrific" but often implies something unbelievable.
* Brilliant: Often used for intellectual or creative achievements.
* Top-notch: Indicates the best possible quality.
* A-one: Similar to "top-notch" but more informal.
* First class: Implies exceptional quality.
Other:
* Impressive: Highlights the impact something has on others.
* Admirable: Expresses approval and respect.
* Worthy: Indicates something deserves praise or recognition.
* Satisfactory: A more neutral word, meaning "good enough."
The best synonym to use will depend on the context and the desired level of formality.