Positive Emotions & Characteristics:
* Serene: Calm, peaceful, tranquil.
* Sincere: Genuine, honest, heartfelt.
* Smiling: Happy, cheerful, joyful.
* Sparkling: Bright, shining, dazzling.
* Splendid: Magnificent, impressive, grand.
* Sweet: Kind, gentle, loving.
* Supportive: Helpful, encouraging, understanding.
* Strong: Powerful, resilient, determined.
* Stupendous: Amazing, incredible, extraordinary.
* Sumptuous: Luxurious, lavish, opulent.
Nature & Beauty:
* Serene: Calm, peaceful, tranquil.
* Sparkling: Bright, shining, dazzling.
* Scented: Fragrant, aromatic, perfumed.
* Soft: Gentle, delicate, smooth.
* Sunny: Bright, cheerful, warm.
Other Nice Words:
* Sage: Wise, knowledgeable, experienced.
* Story: A narrative, tale, account.
* Soulful: Emotional, heartfelt, expressive.
* Serendipitous: Fortunate, unexpected, lucky.
* Stellar: Excellent, outstanding, remarkable.
This is just a small sample. There are many other nice words that start with "S" depending on the specific context you're looking for.