General Wit:
* Quip
* Bon mot
* Repartee
* Aphorism (if it's a short, clever saying)
* Epigram (similar to aphorism, but often more humorous)
* Jest
* Crack
* One-liner
* Comeback (if it's a witty response to something)
* Pun (if it's a humorous use of words with multiple meanings)
* Satire (if it's a witty critique of something)
More Formal:
* Jocularity
* Facetiousness
* Sprightliness
More Informal:
* Wisecrack
* Smart remark
* Sharp retort
* Zinger
The best word to use will depend on the context of the remark itself.