Similar meaning, but more neutral:
* Chuckle
* Giggle
* Titter
More negative connotations:
* Sneer
* Scoff
* Jeer
* Guffaw (can be loud and disrespectful)
* Snicker (more subtle, often malicious)
* Cackle (can imply a harsh, unpleasant sound)
The best synonym depends on the context of the sentence and the intended meaning.