General laughing:
* Chuckling
* Giggling
* Chortling
* Sniggering
* Guffawing
* Cackling
* Tittering
More intense or loud laughing:
* Roaring
* Howling
* Shrieking
* Bellowing
Gentle or amused laughing:
* Smiling
* Grinning
* Beaming
* Chuckling
Sarcastic or mocking laughing:
* Sneering
* Scoffing
* Jeering
* Sniggering
Nervous or uncomfortable laughing:
* Giggling
* Nervous laughter
* Forced laughter
The best synonym for "laughing" will depend on the specific context and the tone you want to convey.