Formal:
* Superb
* Outstanding
* Exceptional
* Magnificent
* Remarkable
* Exemplary
* Extraordinary
* First-rate
* Top-notch
* Premier
Informal:
* Brilliant
* Terrific
* Fantastic
* Awesome
* Amazing
* Wonderful
* Splendid
* Peachy
* Ace
* A cut above
Specific to a certain type of excellence:
* Masterful (for skill)
* Brilliant (for intellect)
* Ingenious (for cleverness)
* Exquisite (for beauty or detail)
* Unparalleled (for uniqueness)
To indicate "another excellent":
* Equally excellent
* Just as good
* No less impressive
* Of similar quality
You can also use a phrase:
* A truly excellent example
* A truly exceptional case
* A truly remarkable achievement
The best choice will depend on the specific situation and the tone you want to convey.