Similar in meaning:
* Giggled
* Smiled
* Laughed softly
* Tittered
* Snickered
* Grinned
* Chortled
* Murmured with amusement
More specific:
* Giggled: A high-pitched, light laugh, often associated with amusement or nervous laughter.
* Snickered: A quiet, suppressed laugh often expressing amusement or derision.
* Chortled: A hearty, jovial laugh, often accompanied by a rumbling sound.
* Tittered: A nervous, restrained laugh, often associated with embarrassment or amusement.
* Murmured with amusement: A quiet, subdued laugh that is barely audible.
The best synonym will depend on the specific context of your sentence and the tone you wish to convey.