Laugh it up
I’m not really a fan of acronyms like LOL (laugh[ing] out loud), so I tend to stick with the written representations of laughing sounds, and the ones I usually use are hahaha (that’s funny!), hehehe (that’s kind of mean!), and hee (cute! squee!).
I’ve always thought the Spanish versions – jajaja, jejeje, jijiji – were really cute, but I have a tendency to read jajaja in a German accent, so it says ‘yes yes yes’.
Here are a few more ways* to show your humour in other languages:
哈哈 / ha ha
嘿嘿 / hei hei
呵呵 / he he
kahkahkah (hahaha from comic books)
eki eki (used in comics, as the older way of laughing)
muhaha (evil laughter)
nihaha (evil laughter)
puhaha, uhaha, zuhaha (used if something’s really funny)
hnhnhn, hmhmhm, chrchrchr (giggle)
My favourite at the moment is a Chinese coworker’s use of hohoho. I don’t think she really means to sound like Santa Claus, but it brightens my day.
*Many of these examples are from WordReference Forums.