The concept trickled down to other MMO's as well, but few actually know the true origin of the word.
Other: Gratz. (congratulations)
Other2: w00t gratz.
Other3: Noice gratz.
Me: ty 8)
guy #2: Ding.
'Ding' messages are usually reserved for friends, or your members of your guild- as people in the general chat show hostility to your level-up.
May appear from time to time as part of another word; eg. 'Ding Dong', 'Ding-a-ling'. etc.
Feelings of joy and happiness usually surround this word, increasing in intensity with higher levelled 'dings'.
'Gary Coleman, I'm only three bars away from a ding'
'I'm going to get my ding then log'