General terms:
* Ebullient: Full of energy and enthusiasm.
* Vivacious: Lively and attractive.
* Effervescent: Sparkling and lively.
* Exuberant: Full of energy and excitement.
* Jovial: Cheerful and good-humored.
* Cheerful: Happy and optimistic.
* Upbeat: Positive and optimistic.
More specific terms:
* Spontaneous: Acting on impulse.
* Gregarious: Fond of company.
* Outgoing: Friendly and extroverted.
* Animated: Full of life and energy.
* Radiant: Shining with happiness.
* Merry: Cheerful and lighthearted.
Informal terms:
* Perky: Lively and cheerful.
* Full of beans: Energetic and lively.
* A breath of fresh air: Someone who is positive and refreshing.
The best word to use will depend on the specific context and the personality of the person you are describing.